Maybe if you made the app free to use and have introduced a karma system , such as the one on StackOverflow, it would maybe make your (ad)venture more successful.

Personally the Flex UI puts me off -- the first impression after clicking the demo button. (The site frontpage looks ok)

I agree that a simple text annotation version would be much better and appealing. (its easier to upload a .doc or .pdf of your work, than scanning it, people who prefer to handwrite are less likely to use any online services than those who prefer doing stuff on their computer when possible