JISC has released the Personal Engagement with Repositories through Social Networking Applications: Final Report.
Here's an excerpt from the project Web site that describes the project:
The Institutional Repository has become the established technology deployed at universities and other institutions to enable scholars to self-archive their research outputs; the PERSoNA team will be embedding social networking tools which allow chat, tagging and bookmarking (amongst other things) within the repository, and encouraging users to comment on their use of our repository and make recommendations amongst each other leading to the onward discovery of further resources.
