I haven't used Twitter yet, because I think that such a high detail of perfunctory microblogging amounts to sensory overload. But recently I've found some very interesting and potentially useful applications of it. There's the Commuter Feed which logs traffic reports for major metro areas. There's also a Google Maps + Twitter mashup that I watched on Super Tuesday to see people's reactions appearing in real-time. Google Maps also had a layer (I think that's the right term) that reported primary results basically in real time per district.
It's still a ton of information that can (and usually will) be condensed and spat out by the mainstream media eventually, but the speed and scope of it all, presented in its raw form, amounts to a new kind of useful social observation. It's interesting that instead of the tool being a single piece of software explicitly designed for a singular purpose, the tool is being procedurally generated, layered, or filtered.