Yahoo recently added Deli.cio.us to it arsenal in order to gain advantage in the search services battle.
Ellyssa Kroski has written an excellent article, The Hive Mind: Folksonomies and User-Based Tagging, which really helped me grasp how to find what I want on the web.
The wisdom of crowds, the hive mind, and the collective intelligence are doing what heretofore only expert catalogers, information architects and website authors have done. They are categorizing and organizing the Internet and determining the user experience, and it’s working. No longer do the experts have the monopoly on this domain; in this new age users have been empowered to determine their own cataloging needs. Metadata is now in the realm of the Everyman.”