I started wondering recently about the iPad and multiple users. We're planning on getting one, and our idea is to try leaving it around the living room. That way someone lounging or watching TV can pick it up to check email, browse the web, or play a game. Much of the rest of the time it could be docked and playing a photo slideshow, basically a nice digital photo frame.
Then I thought about the email part. If I set up my email accounts in the iPad Mail app, won't my email be accessible to anyone who uses the iPad? As far as I know, there isn't any login or anything that would indicate to the iPad OS that one user is different than another.
Mac OS X, of course, has strong multiuser support built in. Settings, preferences, and data are generally saved on a per-user basis. The iPhone supports only one user (where by "user" I'm really talking about a set of data and preferences). This isn't really a problem on the iPhone, since a phone is quite personal; you carry it with you and unless you want to show a friend a new app or let your kid play a game, you're really the only one who uses it.
The "living room" use case I'm imagining, though, means it could be pretty handy for the iPad to be able to tell one family member from another (and maybe guests, too). I could set up my email accounts, my wife could set up hers, etc. Going further, we could customize which apps we like on which pages, or even which apps we like to have show up at all. Starts to sound like we'd have to able to sync each user to a different iTunes setup (different computers or different users on one computer).
Which kind of gets to what I think Apple/Steve Jobs would say about this: not simple enough. People have said the iPad could be the computer for their grandmother to use, and adding multiple users with unique app profiles and syncing with multiple computers pulls the iPad away from the uber-simple ideal.
I imagine the "living room" scenario isn't an uncommon way people would like to use an iPad, but I could be wrong Maybe the issue will never arise for any but a few iPad owners The workaround, I suppose, will be to use web interfaces for email and remember to logout when finished. Seems a shame, though, to not be able to use the Mail app Apple designed just for the iPad.