I picked this up from CNet News.com this evening.  This is the first I had ever heard personally of Microsoft Researcher Chuck Thacker, and was surprised to find he was one of the folks who helped design the original Tablet PC.  Here is a quick blurb from the entire article:

You also helped to design the tablet PC. The concept still has not won over the mass public. How do you see the trend likely playing out over the next five to 10 years?
Thacker: Well, it's actually interesting because when we actually built the tablet at DEC in 1993, we were fairly familiar with what the problems were going to be--and we knew they would be severe. The main one being battery life. The handwriting recognition had to work very well in order for it to be accepted without a keyboard, and I think we came very, very close. I think there's a lot more evolution that is possible there...So in some ways the tablet has been disappointing. But on the other hand, I'm heartened by the fact that it is still a growing market. It just grows every year a little bit, and it's the only tablet-like computing product that it has ever lived in the market for as long as it has. It's now six years old.

Looks like Chuck still believes in Tablet PC, a good idea that has taken a long time being realized!  Go read the whole article -- very interesting guy!