I'd say using Social Networking Sites in education is the big topic of the day in Learning Technology. I'm in the process of setting up an area on Ning for a group of students on placement to use right now.
Dana Boyd is one of the leaders in the academic study of Social Networks and if you're interested in joining the debate about how they could/should/shouldn't be used it's worth having a look at Dana's blog (see the best of page if you're short of time).
If you're interested in current research have a look at the most recent issue of the Journal of Computer Mediated Communication. This journal presents a lot of research relevant to those using communication technologies in education, and this issue covers research on Social Networking Sites in detail.
It's worth subscribing to the Journal's feed if you have a feed reader - and if you've not sort yourself out a Bloglines account or use Feedblitz to get email updates. Just go to the bottom of the Feedblitz homepage and add http://www.blackwell-synergy.com/loi/jcmc as the website address.