A new analysis of data from del.ici.ous shows that, while the number of tags grows roughly in proportion to the growth of content, users can unwittingly provide bridges between networks of seemingly unrelated concepts.
O. Görlitz, S. Sizov, and S. Staab. Proceedings of the Seventh International Workshop on Peer-to-Peer Systems, IPTPS08, Tampa Bay, USA, (February 2008)