Ken Hinckley (The Alpine Inker) works at Microsoft Research and, over the last couple of weeks, he's been running an awesome series of blog posts called Twelve Days of InkSeine.
InkSeine (pronounced ink-sane) is a really cool inking application that Hinckley is working on (which is not yet an official Microsoft product). It's one of the only products around that has been designed for inking and not just a keyboard-and-mouse based product that has inking support. For example, a lot of its commands (like cut, copy, paste, search, etc.) are all pen-flick based and not menu-based.
It's still in private beta but will released to the public in 15 February. To find out more about it, check GBM's InkShow on it. Better yet, once it is available, download and try it. Assuming you have a tablet PC, of course.