If I could use a social media technology in a classroom, I would use Tumblr as a group sharing tool. I think that students would have many meaningful contributions that facilitate learning and allow for the rapid sharing of inspirations, in-progress works and idea exchange.
Tumblr has a built in aggregation that is similar to journaling websites like Livejournal, but is more informal, encouraging of meme sharing. I would hope to have the students all follow each other and me the instructor and creative a collaborative experience. A blog is fairly similar, but I think the easy sharing aspect of Tumblr where links, videos and written content can be mishmashed together is more appealing.