I think the market didn't want tablets in the past because of a lack of a good OS and decent, usable applications.
I've seen tablets used in a medical center, and they had a custom OS and app installed for charting. they loved them.
With the new phone OSes, like the iPhone and Android, we have a good platform that is actually usable for tablets. I know I'm going for an Android tablet when one comes out.
I have a Kindle for reading ebooks, but I've tried looking stuff up on the internet with it, and it sucks at that. I'm liking the idea of having the internet and remote terminals on an Android tablet. It could help with both work and home. Being able to look stuff up on Wowhead while playing WoW, and keeling them both open, would be nice, as well as looking up fixes for various Linux and AIX problems here at work while working on a server would help with work.
The market wasn't there before because of a lack of proper software. Windows XP was never usable on a tablet the way it should have been. With these new OSes, the market will take off now. I'm sure of it.