Welcome to the world of Diigo, one of the leading Top 10 research tools. Diigo is a cloud based information management system that helps you organize relevant facts you find online.
this is the best overview of social bookmarking that I have yet seen - comprehensive but readable. Meant for students it could easily be used with teachers and would make an excellent professional development experience. It provides a well defined way in which researchers can effectively use social bookmarking and annotation by taking on specific roles.