From past experience I have found that discussion boards sometimes work and some classes they are completely empty. It depends on the size of the group (you seem to need a critical mass) and also the nature of the students. Some students are naturally chatty and some are not. Yet according to the news they are all on Facebook and quite a lot are on Twitter.
I have been wondering about the use of Twitter and Facebook in teaching. Resources such as TED produce videos on important issues that they send to Facebook and they are actively commented on and discussed. There are lots of very active discussions on Twitter about blogs and articles in the press, but 140 characters can make discussions difficult and there is a large potential for misunderstanding and "Trolling".
Could they be used to supplement the online learning environment to give up to the minute content?
Could they be used to dynamically alter material?
Could they be used to improve discussion and share ideas?