A couple of months ago I started using Twitter at a computers in education conference (ecoo.org). I'd tried Twitter a couple of times and it hadn't caught - I couldn't see the point in it, but this conference turbocharged the tweets. Following flash mobs to prizes, getting well researched links and ideas from other teachers, backchanneling in presentations... I got hooked.
Twitter is like facebook in that it's a social networking tool, but without the social dead-weight. Follow who you want and lurk, or twit away. If people enjoy it, word spreads and you get a posse. Keep grooming who you follow. After a while it's a steady stream of people you really enjoy reading. Twitter's not about you in the herd, it's about customizing a herd FOR you.
The teacher angle has let me build a PLN, personal learning network. Recently, at another conference, I ran into people I'd been tweeting with over several months. It felt like we already knew each other, but only in a certain way. Filling in the blanks was a wonderful experience, and a great opportunity to pick and choose new people to follow.
I'm still only 6 months into twitter. I've dropped more people than I now follow, and I suspect that I'll top out at about 100, and constantly be grooming out filler. I'm interested in following thoughts and developing PLN, not seeing what a celebrity thinks (rare exceptions: @naomiklien, for obvious reasons, @stephenfry because he broadcasts intelligently).
Twitter feels intimate and direct, while at the same time letting me broadcast far and wide. The idea that it's somehow limiting in scope is inaccurate as well. Twitter and blogs go together like 3 pound lobsters and butter. You can point to deeper thinking in a blog post, or to presentations and mind maps in Prezi, or photos on any number of photo sharing sites (or mashups and collages on glogster, etc etc). Twitter gives you the sign posts, aggregated by the people you trust to follow, and allows you to reciprocate for them.
I just culled the facebook herd and I'm finding it somewhat useful again, but I'm waiting for the blowback from in-law cousin's husbands who want to know why we're no longer friends. We never were dude.