Teachers have also found that Facebook can provide a convenient platform for project assignments, such as creating profiles for characters from Chaucer's Canterbury Tales (or Shakespeare plays). I've recently recommended a classic film "A Canterbury Tale" for English teachers on my movies blog.
Twitter is interesting because it encourages terse writing. A number of people, some of them media personalities like Ashton Kutcher and Anderson Cooper (and many others), have developed followings because of their ability to communicate so much in fewer than 140 characters.
Sometime around 2007 or 2008, after I had stopped subbing, I had some email discussions with the Arlington (VA) school system about getting involved in training in "online reputation". It got bogged down in procedural bureaucracy with all the state regulations of how content can be developed for schools. But I may get back to this initiative again.