I've always found my Tablet PC to be a great tool, for a number of important functions. I've changed jobs recently, and so haven't had as many occasions to take handwritten notes, but that's the most obvious Tablet benefit. Other than that, there are times when even surfing the Web can be more comfortable on a Tablet in portrait mode.
Here's a story about a novelist who uses a Tablet PC in just about every meaningful way, it appears. If you have any interest whatsoever in the Tablet platform, this might tip you over the edge.