Trackballs vs mice vs thumbsticks is more a preference issue than anything else.  Some people swear by them, some people loathe them.

I got my missus a notebook with one of those rubber eraser thingies and a tactile slider thingy (hope you know what I'm talking about) and the first comment was: "Where's the mouse? I can't use these things!"

Having said that, there are companies like this that are using trackballs (and I'm very interested in picking up a set of these controllers to test them out):

http://www.splitfish.com/

But again, a lot of this is preference-based, especially if it is not required. For instance, it took me a while to adjust to a thumbstick when they first came out, but that was the only way to play Mario 64, so I had to bite the bullet (and don't regret it either!). But if I weren't forced to play with thumbstick, I might still be using a D-pad. Kinda like my missus - she doesn't want to "learn" a new input device if she doesn't have to - and she won't. 

Actually, from what I've seen this generation, I believe that manufacturers have decided it's time for not just the consoles to evolve, but the input devices as well.  Just to take a gander:

• Nintendo have never released the same controller twice for their consoles.
• Nintendo took a major gamle with the DS's touchscreen - and it paid off. 
• Sony adds motion sensing with the Sixaxis.
• Nintendo comes out with a console that is largely dependent on motion sensing; in addition to that, they come out with the Nunchuk.
• Nintendo comes out with a Wii Fitness board.
• Sony comes out with the Playstation Eye.
• Sony comes out with the "new and improved" Playstation Eye (v2 I believe)
• Konami releases a few games that are largely dependent on unique aftermarket control devices:
  • Dance Dance Revolution - dance mat
  • DJ Beat - turntables
  • DrumMania - drum kit
• Other developers are releasing game-specific controllers:
  • Guitar Hero
  • Rock Band
• Singstar requires a microphone.
• Steel Batallions was released with a 200$ controller - and sold decently in Japan (a place where such a large device would literally occupy 1/2 your living room).
• DK Bongo game - Bongos!

Peripherals like racing wheels, flight yokes and flight sticks have existed in PC gaming for ages.

I think this all points to a trend: The days of using just a gamepad to play all your games are numbered. Console manufacturers are aware of this. Game developers feel that they are no longer limited to developing games as there is a large market for peripherals to tap into. We are just seeing the start. I don't know what the future may have in store, but I do think it's going to be an exciting ride.

lol

Or Centipede?  But seriously, they've come a long way and could provide mouse-like control with just your thumb.  How can that be a bad thing?

I didn't know that, but I have Mario 64DS and I will try it out. Thanks for the tip. 

I suspect the days for traditional game pads are numbered. Honestly, look at gaming history: how has the basic control pad remain nearly untouched for three decades, as gaming exploded around them? Compare the NES controller to the 360 one. The 360 one has analog sticks and rumble; otherwise, they're effectively the same (the 360 has more buttons, that's about it).

Now, the game pad is attacked from both sides. Casual players seem to be preferring the Wii mote; and I can tell you from experience that high-skill gaming is simply easier with a mouse and keyboard. I expect the traditional controller to become an extended peripheral by the end of next generation. I'm not suggesting the Wii remote will dominate all; I'm saying it's clearly time for a change.

The game pad used to be the controller of choice for more casual gaming -- it's only real competition was the mouse/board, and obviously those have hundreds more buttons and a considerably steeper learning curve. The relatively few buttons allowed for game pads to be the simpler, easier choice. But it's not the simplest, easiest choice any longer, and that's a problem. 

Cringer - I agree that the trackball is more precise for small movements, but what if it needs to be used for an action that a stick performed by holding it down? Flicking it repeatedly would be tiresome, adn simply flicking it hard letting momentum take over would ironically be far too imprecise for even large movements.

Thanks for the great topic, by the way.  

Actually, that's one of the problems I had with the ball for the first few days, but you'd be surprised how quickly the brain learns when to stop the ball at precisely the correct time.  I can now flick that little bastard and land the cursor almost exactly where I need it to end up. With more time, I'm sure it will only get better.

I'm not talking about comparing nine buttons on a phone with a d-pad. I'm talking about replicating all the buttons on a gamepad and incorporating them into a touchscreen. I think there would be an issue.

However, does anyone know how the iPhone works? I've heard some nice things about that screen, but up to now I haven't been able to get my hands on one so everything I know is still unfortunately theoretical.

I agree with the placement. You don't look at the buttons (Well, not the ones familiar to the controls anyhow! I do know people who still look to find the X or Y button because they don't play that frequently.) but again I am not sure if it would hold up under all circumstances (e.g. you shift your thumb a bit off-center to where the quadrants are aligned and you end up losing the "up" quadrant, for example. Sure, you can quickly look at the screen and shift your thumb accordingly to resolve the issue, but that is an issue that wouldn't exist with traditional buttons in the first place. Therefore, while it may improve certain aspects, it isn't without its problems.

The problem with having raised, indented or otherwise physical features on a touchscreen is that you are reducing its flexibility to that of assigned hard buttons (as per my previous reply to cringer8's post) which for me defeats the purpose of having a touchscreen in the first place - why replace buttons with what is essentially another set of buttons? 

I thought playing with those huge trackballs from those coin-ops was a blast! Nothing like the frantic ball spinning to pump up your adrenaline! 

 Hmm, interesting. Like I said elsewhere, I guess it's one of those things you need to experience. I'll look into buying a trackball-mouse and test it out a bit. 

You're absolutely correct.  But I do think having just a flat pad in the shape of a circle would be good enough for gamers.  We have pretty good spatial recognition :)