Surprisingly, it sounds like some of the guesses aren't too far off from the Microsoft Courier concept. I have to say, some of the ideas in that concept of a persistent, everyday computing device sound compelling. Something half way between an interactive moleskin and a kindle.

http://gizmodo.com/5365299/courier-first-details-of-microsof...

I wouldn't be surprised to see apple co-opt some of the interactions of a physical notebook. It would fold up in fit in a small messenger bag pretty easily.