I have not seen too many teachers use social media around this area, none of my CTs did during my placements. I thought that John gave a good talk, he a really good reasons on why to use social media in the classroom. I see potential for it in my classes. The only issue I would have with it is putting in time to make it useful, I have seen many blogs that have just stopped with the last post being in 2009. I did find a directory for all science and math Edublogs:
It does have some useful things.
What are your thoughts of using social media in your classes?