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."
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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)
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B. Krause, A. Hotho, and G. Stumme. Advances in Information Retrieval, 30th European Conference on IR Research, ECIR 2008, 4956, page 101-113. Springer, (2008)
A. Hotho, R. Jäschke, C. Schmitz, and G. Stumme. The Semantic Web: Research and Applications, 3rd European Semantic Web Conference, ESWC 2006, Budva, Montenegro, volume 4011 of Lecture Notes in Computer Science, page 411-426. Berlin / Heidelberg, Springer, (11-14 June 2006)