Recent scholarship challenges the celebratory discourse surrounding Web 2.0. This paper engages with this scholarship to examine critically the implications of academic libraries' presence within commercially owned social media spaces. It considers the apparent contradiction between work to promote the principles of open access and the idea of the commons, and engagement with commercial social media that may be contributing to the enclosure of the commons. It also examines whether the form of participation permitted within commercial social media sites may be limited and subordinating. The paper concludes with possible directions for further research and analysis. (Contains 59 notes.)