There's no reason you couldn't do this today with an iPod. I have home folders on a xserve and can use them anywhere at work, through open directory. The iPod's hard drive is as long lasting as any other hard drive, it's just gets a bad rap because it doesn't like getting dropped, and the ipod can be like a wet bar of soap. You'd just need to set up the home folder location in the NetInfo database for your accounts.