I mentioned this previously in a different thread, but I thought it would be a good idea to summarize here as well. I've had a TabletPC for about 3 years now and used to use the hell out of it. One thing that looked promising, and majorly pushed by M$, was OneNote. Unfortunately, I never really had a use for this and never really used it too much (I have something like 6 legal copies of it, but never found it useful). It was just easier for me to use the pen to enter text directly into MS Word; why bother with OneNote?
Aside from that, I really enjoyed using my PC (a Compaq TC1000). If I were to recommend a Tablet to anyone, I'd say get a slate and stear clear of convertables (you can leave the extra weight/bulk at home and carry a Bluetooth keyboard if you really need one). I think what kept me from using the pen for writing so much was probably getting used to the feel of writing on something that wasn't paper, it just didn't feel right. I wasn't worried about damaging the screen or anything, but it was just too slick and didn't feel natural.
On the UMPC front, I've been definitely keeping my eyes peeled for a nice model that is small, lightweight, useable, convenient, and has a decent battery life. So far I've physically checked out Sony's offerings (still too bulky for my taste), the original Sony was pretty decent, but lacked good resolution. I also checked out one of the earlier UMPC's offered (forgot which brand), but it was bulky, had a smaller screen, and used a dated Transmeta Crusoe processor.
The newer offerings looked cool, but I have yet to see any in person. I'll keep my eyes open and let you know. BTW here is a site I found with quite a few reviews and a lot of pictures:
http://gizmodo.com/gadgets/umpc/
Cant's wait for the Samsung Q1 Ultra!