Earthquakes are a great example. If I feel an earthquake, I might visit a site like that to get the scientific facts about the epicenter and magnitude of the earthquake.

However, there is a totally different kind of value to Twitter posts: instead of data, I'm getting firsthand accounts of who felt it, where, what they were doing at the time, and what effect it had on their life. Yes, this information is (obviously) anecdotal, but its also interesting, informative and immediate.

That doesn't update every second of every minute of every day. Verifying immediately that you did in fact feel an earthquake is a perfect example of twitter's power. As a San Francisco resident I can tell you this definitively.