I didn't mention that I have watched Twitter occasionally, but for purely unprofessional reasons!! I followed Lance Armstrong and some other cyclists through the Tour and it was somewhat fascinating to hear their short accounts of the day, and being able to "trust" the account since it hadn't been spun by the media. I cannot possibly think of anyone that would be vaguely interested in my posts though.
And Ning! Perhaps I am just being attracted to something listed as more professional. But I typed in engineers and got a page of credible sounding groups. And then of course dozens of cool (well I think so, perhaps you would call them nerdy) maths teacher groups.