Here's an article that describes a set of requirements for social networking tools for researchers -- in biomed, but most reqs are probably generalizable to other fields:

Schleyer, T., et al. (2008). Facebook for Scientists: Requirements and Services for Optimizing How Scientific Collaborations Are Established. Journal of Medical Internet Research, 10(3). http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2553246