Educational Value of Social Networking sites

Okay - it is my turn. I need data from others on the educational value of social networking sites to make available to our principals as they decide "to block" or "not to block". These links have already been made available to them:

http://blog.absolute.com/educational-benefits-of-social-networking/

http://boardbuzz.nsba.org/discussions/archive/session.10172007.edbenefits.php

http://aquaculturepda.edublogs.org/tag/educational-networking/

If you have other information or sites that I should make available to them, would you please post them for me?

Thanks to you all.

Connie