Fantastic! And it's nice to see a new contribution to ipdf!
I haven't had a chance to try this yet, but I'm very excited about it. It would be VERY useful. If you add functionality to make comments for each bookmark, I wonder if they could be little handwriting-boxes? That way we wouldn't have to mess around with the keyboard. Although probably a text-box would be easier to implement.
Anyway, excellent work, and I'm looking forward to trying it!