I don't have time to test the actual app right now (it seems like a great service). So my only review could be about the front page, which is pretty, but the features animation (images fading & sliding in) is not implemented well. the previous image fades very slowly and for no apparent reason, every time a new image slides in, my browser lags (it could be my browser though; Safari 5.2 beta).

Also, I think your sample documents are not good examples of what your app can do, and a couple of them (1st, 2nd) are kinda low resolution.