You may have noticed I had some Copious Spare Time (TM) recently, although that's fast changing. In any event, I spent some of that time playing with my PSP, a device that I have previously equated with a PARCTab. In that time, I upgraded my PSP with a 2GB Memory Stick. I've had a lot of fun throwing tons of media on it and using the PSP like an oversized iPod. Note though that said "iPod" has two forms of removable media (Memory Stick and UMD), not to mention built-in WiFi. And in exchange for the size differential, you actually get pretty good battery life when using the WiFi, which normally sucks with PDA-like devices.
I also discovered that my PSP headphones also serve as a little remote control. Combined with the multitude of game playing controls onboard, the PSP would make a great platform for developing ubicomp systems and applications.
Unfortunately, I spoke too soon about being open to development. The one tool I pointed to, Adventure Maker really just creates HTML browser applications, and makes them easily accessible to the built-in PSP browser. Not a trivial achievement, but a pretty low ceiling. Apparently there are actually sophisticated tools and middleware for the PSP, but you have to be a licensed PSP developer to get a hold of them. I'm guessing that this is not an easy trick, and impossible if you can't demonstrate a multimillion dollar revenue stream for Sony.
I wonder, however, if a resarch group teamed with a previously licensed developer could make any headway. Hmmmmm....
I guess the fallback is the rich internet application route, depending on how well the PSP browser supports DHTML and/or Flash.