Some interesting data-driven findings about Twitter are revealed in this study conducted by British psychologists.
I enjoyed the description of "informers vs. meformers" as it relates to tweet content. I find that my own social graph has a fairly balanced ratio of users who fall into each category.
I'd propose that Twitter as a source of breaking news or emergency response will only continue to grow in importance. When I want information about something that JUST happened, I always search Twitter first. Granted, you may end up with content that proves not to be 100% accurate after the dust settles, but no less so than information you'd gather from other sources. That's just the nature of gathering information quickly.