Earlier quoted context omitted.
What you're talking about in the last paragraph is sentiment analysis. This is really cool stuff, but it's tricky. Even if you have 2 humans do sentiment analysis independently, they agree with each other only 70% of the time. Computers tend to do worse, of course. What makes it extra challenging is that tweets are short, so you have wide error bars on the sorts of math you'd depend on in larger corpuses. I think you…
Btw, here's an example of somebody trying to do sentiment analysis on tweets: http://www.sentiment140.com/search?hl=en&query=romney .
Thank you, sentiment analysis - I just love that term.