Twitter as a reporting tool

OK so I hope everyone knows what Twitter, the microblogging platform, is now.  Jeff Jarvis says he's heard  of some interesting ways it could be an early warning tool -- like a police scanner -- for news organizations looking for breaking news:

I’ve also seen work by the BBC and Reuters, among others, in trying to extract news from Twitter (and other us-created media) by looking for the hot words of news (explosion, evacuate…). This becomes a sort of canary in the news mine.