I don't use it personally, but we have a Twitter thing set up for Carol. We use some of the various tools, so when something like her Blog is updated, it automatically sends out a "Tweet" on Twitter. She has a big following on it, and you can defiantly see the traffic bumps when she writes something to do with her site. It's a mixture of the same old mindless Twitter stuff and spam. But as long as it works, we'll keep using it.
It's just another tool that when used properly does work. We always jump on the newest bandwagons as soon as they start. You have to be foolish not to with what we do! All these flavours of the month do bring in traffic, and without having to pay an affiliate!
The trick is to use them while they work, and when you see the slow down, dump them and move on to the "next big thing".