I do Facebook, but not Twitter (at the request of my 20-something kids). I'll "friend" former students on my personal account, but not current students, just as a matter of form.
If my library/school had a Facebook account, it could be used to put out information quickly, highlight new services, answer reference questions, and such.
For the dual-credit classes and others taught on campus by non-ISD personnel, having a back-channel capability would be critical, since questions from students so often arise after class time is over. Backchannelling could also facilitate study groups, project brainstorming, etc.
But as long as the average ISD and its administrators put the big nix on accessing social networking sites at school, none of these simple-to-implement scenarios will take place. As well-meaning, but reactionary, school officials continue to deny that Facebook & Twitter have any educational validity, their districts and schools will continue to present an environment that is further and further removed from the ways that so many of our youngsters learn and discover information today. And what about the future??