Well, I have to say, prior to the class on Twitter, I had an extremely negative opinion of the medium. I thought it was just another forum for people to publish every thought that came into their heads, without consideration or critical thinking. I signed up for it because I felt that I needed to give it a fair chance, and that I should better understand how it can be used in the classroom.
At this time I would say that Twitter does have some positives: it allows many points of view to be expressed simultaneously without the usual ensuing cacophony, it transmits more information (about the opinions, knowledge of others) in a shorter amount of time, and provides an easy way for the teacher to keep track of who's paying attention and who isn't, who's struggling and who isn't.
Basically, I think Twitter is like a lot of things, useful and good in moderation.