With web contents being generated and shared at an ever-increasing pace, a number of approaches to effectively control and retrieve contents have been developed. Social tagging is a widely implemented method for classifying contents resulting from the dispersed activities of users. Social bookmarking services (SBM) is a web service with the purpose of making information generally available on a shared basis. Accumulation of tags on SBM occurs mainly without inviting the collaboration of others, but on the basis of activities satisfying individual self-interest. SBM is in fact the optimal web platform utilizing the sum of such activities for the formation of commons.