  Tagging communities represent a subclass of a broader class of user-generated
content-sharing online communities. In such communities users introduce and tag
content for later use. Although recent studies advocate and attempt to harness
social knowledge in this context by exploiting collaboration among users,
little research has been done to quantify the current level of user
collaboration in these communities. This paper introduces two metrics to
quantify the level of collaboration: content reuse and shared interest. Using
these two metrics, this paper shows that the current level of collaboration in
CiteULike and Connotea is consistently low, which significantly limits the
potential of harnessing the social knowledge in communities. This study also
discusses implications of these findings in the context of recommendation and
reputation systems.
