New Ajax social bookmark URL(you can see with what tags one have bookmarked you) and tag search. Says it will be adding more social bookmarking query services almost daily.
"In folksonomies (...) we get to discover content based on who is tagging it. This is powerful because now we can judge content in terms of who (...), and not just how relevant it might be to some algorithm that doesn’t take into account who-knows-who."
B. Krause, A. Hotho, and G. Stumme. Proceedings of the IR research, 30th European conference on Advances in information retrieval, page 101--113. Berlin, Heidelberg, Springer-Verlag, (2008)
R. Wetzker, C. Zimmermann, C. Bauckhage, and S. Albayrak. WSDM '10: Proceedings of the Third ACM International Conference on Web Search and Data Mining, page 71--80. New York, NY, USA, ACM, (2010)
B. Krause, R. Jäschke, A. Hotho, and G. Stumme. HT '08: Proceedings of the Nineteenth ACM Conference on Hypertext and Hypermedia, page 157--166. New York, NY, USA, ACM, (2008)
B. Krause, R. Jäschke, A. Hotho, and G. Stumme. HT '08: Proceedings of the Nineteenth ACM Conference on Hypertext and Hypermedia, page 157-166. New York, NY, USA, ACM, (2008)