Without much surprise there has been significant movement within some of the social networks over the course of the last year. Brian Chappell from Ignite Social Media has put together a comprehensive report based on data from all major social networks existing on the web.
K. Wolff. Proceedings of the 12th International Conference on Conceptual Structures (ICCS 2004), volume 3127 of Lecture Notes in Computer Science, page 126-141. Springer, (2004)