This is my latest endeavor. I thought it would appeal nicely to the HN crowd who read heavily online. Let me know what you think - I'm here to answer any questions.
1. Can you export your data? JSON preferred.
2. Is there an API?
3. How does it compare to http://okfnlabs.org/annotator/, which is free, open source and distributed?
2. Again, not yet. What features would you like to see in an API?
3. The main difference is the social value. I can easily make annotations and share them with you, see what my friends are bookmarking and highlighting. We're looking to build a community, rather than just an annotation tool.