From Perdue University comes ThoughtArk, a collaborative online scholarly bibliographic bookmarking site. From their ‘About’ page:
An open source, free web application and collaborative space that utilizes the search behaviors of the users to determine the value of various bibliographic resources. It is at the same time a concept based social networking space. Users can identify people with similar interests and interact with them and their resources. Finally, the sources once identified can be collated and cited in papers written and published through ThoughtArk.