del.icio.us is a popular social bookmarking website. It allows users to bookmark, tag, and share websites, plus offers several more advanced features, including rss and atom feeds, users can send links to other users, and users can follow their 'friends links. It is free to use.
Social bookmarking sites such as del.icio.us can be used in many ways to facilitate and aid study and learning.
For example, you can see all sites with particular tags, e.g., by going to http://del.icio.us/tag/socialbookmarking.
Please add more ways in which del.icio.us can be used in education and research.