I take notes using a Livescribe Echo pen as I am reading. It gets OCRd about 90% correctly. I fix the last 10% manually. The whole point of taking the notes is because I have a horrible memory :).
I always wanted to build something better for taking notes (many ideas from social, to comparing notes etc.), I think that could be very useful.
I wish at least the Kindle had an API to get my highlights out.