Logitech IO Personal Digital Pen...it was the best I could do in my zeal to get a Tablet PC. I figured, hey, why not spend the $99 bucks (I had a 50% off coupon) and pretend? :) I've got Wacom Tablets (in additional to Microsoft optical mice and trackballs - I believe STRONGLY in multiple input devices) at home and work that I use for signatures, and graphical detail work.
Here's another fellow's review of the Logitech IO Digital Pen...I tend to agree with him. It's a smidge spendy, a little bulky, but it is FANTASTICALLY accurate. So much so, it's slightly creepy. It uses a technology from Anoto (How does it work?) that is rockin' sweet. One of those ideas I should have had.
Anyway, I'm using it to takes notes for Physics and I'm impressed to say the least. It's clearly an early adopter technology, but with support from paper vendors (for the paper with the special printed dot pattern) like Cambridge and Mead, I wouldn't be surprise if this caught on in the next 2-5 years. If only Microsoft and all these guys can decide on the XML format for Digital Ink.
Comparing all the different ideas on how to track the pen, I'm surprised so many companies are trying to triangulate with infrared and such...changing the paper seems IMHO to be the obvious choice.