Library 2.0 literature has described many of the possibilities Web 2.0 technologies offer to libraries. Case studies have assessed local use, but no studies have measured the Library 2.0 phenomenon by searching public social networking sites. This study used library-specific terms to search public social networking sites, blog search engines, and social bookmarking sites for activity associated with librarians and library users. Blog search data about the recentness of activity or the popularity of a blog post indicate that Library 2.0 technology has many early adopters but provides less evidence of sustained use. The results follow a curve resembling the 80/20 rule and also resemble Chris Anderson's "long tail" effect, in which very few authors create the vast amount of content. These exploratory results can be used as a starting point for future studies. Librarians who use tags to describe Web-based content might use these findings to select more effective tags. Librarians implementing a blog or a social networking presence might use this study to balance the benefits with the amount of work required to maintain an up-to-date presence. (Contains 14 tables and 1 figure.)