It reminded me of the the review tools in Microsoft Word which I've used a few times with students - someone sends me a Word document and I add comments and suggested edits. The review tools can track changes I make as well as highlighting sections and adding notes in the margin. I can then send the annotated Word document back to the author and a conversation grows around the original document and our comments. When I first started using this feature of Word, I thought it would be great if you could do that with web pages. Imagine being able to get a class of students to collaborate on a web page: to highlighting sections, share their understanding, ask questions and add extra information. With diigo, that's exactly what you could do.Add to that online social bookmarking (which can be linked to other bookmarking services such as del.icio.us), the ability to highlight any text on a page and search for it on a range of search services using a pop-up menu, to blog about a page and link non-diigo users to your annotations on that page (this blog posted was created using the diigo Blog this tool) and a host of other features ...and you have a stunningly valuable educational tool.