Going system by system, I'm going to highlight all of their features.  I'll point out some key differences, too.  From there, everyone will get a fair analysis of what each system offers.  If I leave anything out, feel free to point it out.  I'll post no opinion.  Just facts.

First up:  The Xbox 360.  When you fire it up, this is what you get:

-Spotlight: Specially themed gaming experiences appear.  Today, it's all about Halloween.  New games that are available, or new DLC is also highlighted.  Also, scheduled events (like Ladies Night or Game With Fame -where you can play with game developers or music groups and such) are shown.  Any new Xbox information is displayed here, too.  Last, but not least is the "Deal of the Week" where Gold members can get discounts on whatever DLC is on sale that week.   Press up on the d-pad for:

-My XBOX: From here, you get the option to play your current game, install it to the hard drive, view your profile, view your Achievments in every game you've ever played, or launch one of your downloaded games.  Your downloaded video library, downloaded/saved music library (you can change the background music to any game in your library to this music), photos (you can customize your wallpaper here), and console settings are here, too.  And if you have a PC, this is where you can connect to it to share content or browse the web.  I never use that option. 

In your profile, you can create your avatar, set up your theme, write your profile, set up who can view your information (when you're online, what you're playing, who your friends are, who their friends are, etc.) and your gamer pic.  People on my friends list get a picture of my true face.  Everyone else sees Max from "Sam and Max".  Press up on the d-pad and you're taken to:

-Game Marketplace: New arrivals to the arcade or the low price/low quality (some cost a $1 but you get what you pay for) Community Games/Indie Games are shown here.  You get your top rated and most popular downloads queue here, too.  You can download retail games like Dead Space or Fable 2 here as well as any add-ons that may catch your eye.  Demos for hundreds of retail games and every single Arcade game ever are available for download.  This is also where your Themes and Gamer pics are purchased.  Some are free, though.  There's also a coming soon section but I don't use that very much.  Next up is:

-Video Marketplace: If you have Netflix, this is where you watch it.  You don't even need a computer.  Movie Rentals (no purchases, but I never buy digital movies anyway), Music videos (these can be purchased for about $2), TV shows, exclusive programs, internet videos, game related videos, and such are available here.  You can watch videos with your friends, and talk to them as if they were in the same room.  Game videos are also available in the Game Marketplace.  Up from there is:

-Friends:  An avatar/caricature of your friends are shown here.  You can view their motto, send them a message, game invite,video or party chat as well.  The profile is super detailed.  You can see when they were last online, what they're playing, where they are in the game that they're playing, who they're playing with, when they last played a game, what their achievements are, etc.  Up from there is:

-Inside Xbox:  Insider videos, tips, behind the scenes videos, and a spotlighted gamer profile are found here.  Hot new games are given special treatment here, as Major Mike tells you about some of the tips of the trade.  Other older, free videos are found here, too.

-Events:  Scheduled events are shown here.  Co-op night for certain games, so you're guaranteed to find someone with the same interests as you, gaming with celebrities (again), gaming with developers, and contests are in this area.  Up next is:

-The Welcome:  It's pretty useless and you can turn this section off.

As a side note

-You can download, even when the console is turned off.

-You can view the last 50 people who you've played with and rate them, "prefer" or "avoid"

-You can rate all contents and games (much like a youtube video)

-You can chat with people on your friends list regardless of what game they're playing.

-installing a game to the hard drive makes the console virtually silent.  It also improves performance in most games.

-backwards compatible with hundreds of original XBOX games (HDD required).

Some of these things are free, but you get the idea.

Odd man out because:  No Wi-Fi, No motion control, no SD Card support, No internal Web Browser.  No portable gaming little brother (despite being able to interface with a PSP and Zune). Annual subscription fee.

Next up is the PS3.  Upon firing up the console, this is what you get:

-Users:  A listing of authorized users.  My pic is a pic of Super Mario.  My daughter has a pic of herself.  Awesome!  This is pretty much where you choose the profile of the person who will be playing.  From there, to the right, you get your:

-Settings: You can set up your video to play, one after another (Nice feature!), if your PS3 has backwards compatibility, you can set up older games to display in HD or load faster.  This is also where you set up your themes, Remote Play (for PSP owners), and Network settings.  The PS3 has Wi-Fi.  I use a wired connection.  To the right of that, you get:

-Photos:  If you have an SD card, Memory stick Duo, or a cell phone, you can connect them here.  A cool bonus is that with the PS3 browser, you can save pretty much any image from the net to your hard drive.  You can set up slide shows from here.  You can also set up any photo as your background.

-Music:  Like the 360, you can rip CD's.  Also, like the 360, there's a cool selection of background visuals that play in sync with the music.  You can also download music from the internet and save it to your PS3.  SD Cards and MS Duo music is also supported.  To the right of that is:

-Video:  Pretty straight forward.  All of your downloaded videos, as well as your DVD's and Blu-Rays are viewable here.  Unlike the 360, you can view downloaded video one after another without having to select them.  The next video plays instantly.  Once again,  SD cards and Memory Stick Duo support is available.  One step to the right takes you to:

-Games:  Your PS1/PS2 "memory cards" are found here.  Also, your trophy collection is in this area.  From here, you can launch your downloaded and disc based games.  They're broken up into PSN/PS3, PSP, and PS1 sections for easy access.

-Network:  If you have a PSP, you can connect it here, and use some of your PS3 content.  Your internet browser is here, as well.  It's not perfect, but it does what you need it too.  I will state that some sites (Yahoo, MSN, Myspace, Facebook, etc.) are gimped here.  I'm just saying.  Still, it's better than you'd expect.  Video from most sites are flawless.  You can also download some video and music directly from the net to the PS3 hard drive.  This is also where you find "Life With Playstation" (formerly known as Folding Home).  Yes.  Your PS3 is curing cancer.

-Playstation Network:  It's like "Network" but this time, it says PLAYSTATION in front of it!  Playstation Network places you into position to manage your account.  Like the 360, you can add your credit card for easy purchases.  Unlike the 360, if your purchase costs $5.13, your purchase will only be $5.13 and not 625 Microsoft points or whatever.  Personally, I like this.  There is a "What's New" section here, too. 

This is also where you can find the beloved/ hated Playstation Home.  It's pretty much like Myspace with avatars and no hot women.  Home is pretty much what you make it.  There are a few free games there  and clothing and such to personalize your avatar and his home in Home.  Most of this stuff costs money, though.  And, like the 360, you can win free stuff for your avatar by playing games.

The Playstation Store is here, too.  All of your New Releases are here.  Like the 360, you can go about searching in a variety of different ways (newest to oldest, alphabetical order, etc.)  You can buy your downloadable games, get your add-ons, try your demos, and such on the Game side or you can rent/buy movies or TV shows from the Video side.  While I must admit that the 360 has many times more content that the PS3 in its marketplace (demos, video, add-ons), the 360 has been around longer.  Besides, how much content does one actually need?

-Friends:  In this area, it shows "Players Met".  Mine says "No players have been found".  I still don't know why.  I've played a ton of games online.  Oh well.   If you have a Mic or a Camera, this is where you can innitiate a private chat.  This is also where you can view your friends and their profiles.  You don't get much info, though.  Just who they are and possibly a sentence about them, and their language.  The choice of "Gamer Pics" are very small, when compared to Xbox 360.  Not a huge point, but one that bothered me.  The PS3 also tells who is online, what they're playying, and displays their trophies, if you want to view that info. 

-One thing I'd like to point out is this:  If "Mister X" is online on the PS3, playing Lego Indiana Jones, the PS3 will say "Lego Indiana Jones".  If your friend, "Mister X" were online playing Lego Indiana Jones on the 360, the 360 will say "Online Playing Lego Indiana Jones with Mister Y Co-Op, level 2 about to steal some treasure -Joinable".  Just something else I want to point out.

-All in all, this is a ton of content for free.

-The PS3 is the only console with Wi-Fi AND wired connections, right out of the box

-The PS3 is the only console that saves your recieved AND sent messages to your friends.  The Wii only saves recieved.  The 360 doesn't save sent messages and deletes received messages after 30 days.

-The PS3 has an animated preview of any blu-ray game inside of the system, as well as PSN downloads.  The 360 and Wii only have static photos/previews.

-It supports USB based PC controllers (or so I'm told......)

-Some versions of the console are backwards compatible with Playstation 2 games.

-Supports non-proprietary Hard Disk Drives for relatively cheap and easy upgrades.

-Online multiplayer is free

Odd man out because:  It's black.  No huge brick on it's adapter. Blu-Ray support.

Nintendo Wii

When you fire up the Wii, this is what you get yourself into:

*note*  The Wii Menu can be arranged in any order.  Here's mine-

-Games Channel:  Launch your Nintendo Wii or Gamecube disc based game from here.

-Wii Shop Channel:  This is were you download from a rather large selection of Wii Ware, Neo-Geo, Nintendo Entertainment System, Super Nintendo, Sega Genesis, Turbo Grafx 16, Neo Geo, Arcade, etc. games.  They are pretty much available as they were originally, glitches and all.  Still, it's an old school gamer's paradise.  My Wii says that an update is available and I don't feel like updating right now, so.  Yeah.  Also, the Wii is the only one of the big three that offers absolutely no background downloading at all.  Mario runs across the screen grabbing coins as the game downloads.  I've seen Mario grab 11 billion dollars worth of coins.  I wonder what he does with it all.

-Internet Channel:  Strangely, when you fire this channel up, it says "Internet Channel internet".  A little redundant, isn't it?  Anyway, this is where you find your Wii browser.  It's a little limited, but it's fast as lightening.  Faster than my PC, sometimes.  It does suffer from limited memory, though.  It also can't copy and paste, as far as I know.  Still, it plays video from a lot of sites, and it does about what you'd expect.  Some video and pics won't show up on it, though.

-Mii Channel:  Here's where your avatar hangs out with other avatars.  When you're not looking, they conspire to kill you and escape.  Cute little guys!  Here's where you make your little guy, or receive Miis from your friends.  They often run around endlessly in the Mii Parade, too.  It's a cute distraction.

-Forecast Channel:  I actually use this thing a lot.  It's a pretty bare bones weather forecast.  Still, if you want to play your week, it's always available in a heart beat.  I hear that there are games that actually use the weather to effect gameplay.  Weather this is an idea that was never used or not, I don't know.  None of my games feature this, though.

-Pokemon Puzzle League:  Great game.  You should buy it.  I think I'll leave my downloaded games channels out of this, from now on.......

-News Channel:  Instant access to the news that effects your world.  It's broken down into different sections: National News, International News, Sports, Arts/Entertainment, Business, Science, and Technology.  I actually use it more than Yahoo! News.

-Check Mii Out Channel:  A nice little diversion and a good way to get some cool Miis.  All you do is vote on which user created Mii matches a particular theme.  If you're so inclined, you can enter your own shitty Mii and lose to some guy who can make a Mii look like Optimus Prime.  I quit competing a long time ago.  You get ratings based on how well you vote with the population.  Go ahead.  Conform to popular opinion!!

-Everybody Votes Channel:  It's simple.  Your Mii is trying to get home to his family and get some sleep.  Unfortunately, the guy from "Saw" wants you to play a little game.  He's going to ask you a series of questions like "Which tastes better?  Apples or Hamburgers".  Of course, this is an opinion and there is no wrong answer.  Except for the fact that THERE IS A WRONG ANSWER.  And anytime you choose what the majority of the voters choose, you get on step closer to going home.  Anytime you choose the "wrong" answer, your Mii gets pushed farther back.  I used to play this game every couple of days.......then, my Mii died from exhaustion.

-Photo Channel:  Hidden way in the back of my Wii Menu is the Photo Channel.  There are photos stored there that will get me killed.  I can't copy them because the Wii won't support that option.  I can't delete them because of the memories!  Damn, I wish I hadn't lost that SD card with the originals.  Anyway, the Wii lets you draw on and save your artwork.  It's more fun than you'd think.  You can also have the Wii cut the photo up, and try to put it back together while you race against the clock.  Like the PS3, various filters and background music is available and can be selected during your slide show.

-Wii Message Board:  All of your recieved messages, photos posted, and what you played/did on a particular day is posted here.

-Nintendo Channel:  A recent addition, this allows you to view videos of new Nintendo console releases, lets you download demos to your Nintendo DS, lets you critique games, tells you which games you've been playing and for how long, and is pretty much your one stop shop for all things Nintendo.  It's my favorite part of the Wii interface experience.

If you have music on an SD card, you can play it on the Wii on this channel, too.  Some video format is supported but I have yet to watch a video on the Photo Channel.

Also of note:

-The Wii has various options for internet access (Wii Connect 24, Wireless Wi-Fi), parental controls, System Naming (Mine is called N7!) and it supports SD cards for memory expansion.

-The Wii lets you gift a games to your friends. 

Odd man out because:  No built in Ethernet Cable support, no hard drive, no CD support, no DVD support, 100% backwards compatible with prior generation, not HD.

the Video marketplace is called Zune market place now.

I was so tempted to write combo breaker, I WAS SO TEMPTED! I would have made it in between ps3 and wii.

Oh come one....there has to be SOMETHING you can say about the PS3!...  : )

How dare you say that about the Welcome section! Thank you WoW user ignore script

Interesting, however for me it is mostly about the games. As I own both consoles I think I'm not really biased, but it should be noted that I prefer the PS3.

Xbox 360:
Like: - The controller is better when it comes to the analogue sticks and the triggers, but the face buttons are better on the PS3.
- Great games, for me esp left4dead, dead rising, gears 1+2 and a few more I have probably forgot

Don't like: - That you have to pay for xbox live gold, and to get wifi
- It is big, ugly and noisy

PS3:
Like: - Nice hardware, quiet and better looking
- Starting to get some great games (not counting multiplat)
- blu-ray
- like the user interface (xmb) alot better than xbox360

Don't like: - Can't really think of anything except the lack of some titles

Wii:
Like: - Some great nintendo games
- Interesting controller
- Small and quiet hardware

Don't like: - too few great games, and a LOT of crap
- Last gen graphics

To conclude, I mostly use my PS3. Xbox360 and Wii spend most of their time in the closet, Wii comes out for great nintendo games, and xbox360 for playing Rez HD or Braid (and left4dead 2 I'm sure). Use my PS3 almost every day for playing games including multiplats, and to watch movies. Don't want to get rid of the other two though.

Sounds like a cluttered mess with useless shit and spam. Nice job MS.

"Sounds like" but have you seen it?

you are right about the spam though, there are alot of adverts and useless stuff, but its no where "Cluttered mess" its actually user friendly.