ReadWriteWeb

Twitter was originally designed as an app that would allow people to share information about what they were doing within a distributed group setting. It's something akin to a collection of automatically forming email discussion lists (except not via email). The benefit of this is that people can receive and send information within a group very quickly. That's why Twitter has become such an important source of breaking news, and it's also why helpful consumer information apps like Commuter Feed are possible.