Here's an example of our AJUSD students using it in the classroom.
Diigo info and a quick guide to how to highlight and add a stickynote, and other annotations as well.
Fabulous video with Diigo tutorials on:
general info; lists; different ways to search through your bookmarks; using the Diigolet; etc.
(This is a Common Core Writing Research Standard and a collaboration standard)
This website has a great intro to using it in the classroom, sample lesson plans and videos