edutagger is a social bookmarking service for K-12 learners and educators, allowing you to store your web links online and share them with others, all within an educational context.
eHub is a constantly updated resource of web applications, services or sites with a focus on next generation web (web 2.0), social software, blogging, Ajax, Ruby on Rails, location mapping, open source, folksonomy, design and digital media sharing.
"The future co-existence of controlled vocabularies and collaborative tagging is predicted, with each appropriate for use within distinct information contexts: formal and informal."
R. Abbasi, S. Chernov, W. Nejdl, R. Paiu, and S. Staab. Advances in Information Retrieval, volume 5478 of Lecture Notes in Computer Science, page 654--661. Springer Berlin / Heidelberg, (2009)
A. Hotho, R. Jäschke, C. Schmitz, and G. Stumme. Proceedings of the 3rd European Semantic Web Conference, page 411-426. Budva, Montenegro, Springer, (June 2006)