If you have more than one account it asks you to chose which one as soon as you turn on the console. All saves files, friends, messages, settings etc. are kept seperate.

You can make it auto sign in to one user if you want.

Well, basically, if it's for the internet browser or something, just have the most frequent user have the account auto-sign in.

If your wife then wants to (I don't know) do a little Resistance 2 multiplayer, then she'll have to log YOU out, and log herself in.

@ kyliedog: I guess it's his opinion, like your "MM are level-dictators"-opinion ;)

It is my opinion that the Earth is flat, and that chocolate was invented by the government as a mind control substance...

hey, I never said that his opinion was valid, just that it was his opinion.

@Papflesje&OkeyDokey: Thank you.
It works in a way just as i thought it would.
Since i wanted to point out to Munkeh what ookaze meant in the first page, i think we have enough information about how the PS3 deal with online and offline.

As ookaze said, that Wii has seamless online, it means that you don't have any logging in/out to do. You access the online features the same way you access offline features. If you want to play a game online or offline, you pick up your save file (this is the idea of having game specific friendcodes, btw.). If you want to enter Mii Channel or Photo Channel, you enter it the same way you enter Internet Channel or Nintendo Channel. You don't have any "online" menu or section. All the online and offline channels are mixed in the menu, in an order you want them to be in. And even when you have WiiConnect24 on, it still stays online, no connecting or anything similar.
In the same fashion that the Disc Channel shows you which game you have in the console, the online channels show you the latest news headlines, current weather, latest additions to online shop, about new competition. Even the offline channels give you new information, such as Wii Fit Channel telling you how long since the last time you played Wii Fit. You don't need to log in or start the application to know "what's new".