From Scoble, via James, comes the question of who innovated the tablet PC. (Depends on what the meaning of "is" is, probably. 8*)
Certainly the idea goes back at least to Alan Kay's Dynabook in the 1960s.
Going back 12 years (oh---my---god) we will find the Momenta product, a Smalltalk-based tablet PC (1991, mind you) that was a little ahead of its time (and from a horribly mismanaged start-up as I recall).