An interesting report from the National Schools Board Association says that "online social networking is now so deeply embedded in the lifestyles of tweens and teens that it rivals television for their attention" and that "an astonishing 96 percent of students with online access report that they have ever used any social networking technologies, such as chatting, text messaging, blogging and visiting online communities, such as Facebook"
The report lists the activities that tweens and teens say they do at least weekly:

And in terms of using social networking for educational purposes:
59% say they talk about any education related topics, including college or college planning; learning outside of school; news; careers or jobs; politics, ideas, religion or morals; and schoolwork
50% say they talk specifically about schoolwork
Creating and Connecting: Research and Guidelines on Online Social - and Education - Networking [PDF]
[PS: Facebook ranked highly in our Top 100 Tools List, which is further evidence to suggest that social networking is becoming a key "educational" tool]
