I didn't know what to make of Twitter. If you've sort of missed out on what it is, figure a cross between blogging and updating your IM away message. It's all about sort of micro-updates about what you're doing. It's limited to 140 characters, which forces you to stay concise, and allows you to do updates via a text message, or the web, or any sort of app you want to build that interfaces with Twitter.
Then, people can "follow" you or "friend" you, just like on pretty much any social network, and get updated to what you're doing. People can have updates sent to their phone, IM, or just over the web (HTML or RSS). It sounds so egotistic and silly: who would want to know what you're doing all the time? Do people care that much?
It sounded so stupid. I checked out some of the more famous Twitterings (?) online and I wasn't sold. Then, I went to Vegas. I wanted to send notes back to people at home--you know, just silly stuff. I signed up for Twitter and gave it a shot. I really haven't stopped using it since. The ability to just send a text message off to a phone number and have it update a little blog is pretty powerful, and can (depending on how many people use Twitter in your little network) be pretty helpful if you're looking for some quick info from your friends.
I can think of a whole bunch of other uses (some of which I'm going to try to implement at work ... we'll see how that goes), but, fundamentally, it can be a useful way to get some information out when you don't have enough in your brain to do anything too big (like update your blog ...).
I'm guessing it'll fade out, but Twitter is a handy fad. I'd almost like to sync my Twitter status to my IM status/info, so people can sort of follow me however they'd like.
The other good thing about Twitter is that it's one way. It's only outward communication (though you can use it to sort of carry on a conversation) which is nice, particularly these days when there's just so much data flying at you (for instance, at work, I'm on 4 IM networks, plus two email accounts, plus normal web stuff). Twitter's unidirectional (monodirectional?): I just spew and I don't have to listen back. Not very friendly, but sometimes it's what you need.
I'm going to try to add my Twitter feed to my blog (look that way ---->). We'll see how it goes.