Here's a nifty new application in sentiment analysis: the Daily Beast's "Election Oracle." It's based on an engine called WiseWindow, which apparently scrapes the Web in real time, searching for content relevant to all the midterm elections, then makes predictions. One interesting touch is that DailyBeast pipes in RealClearPolitics' latest poll numbers, inviting head-to-head comparisons.
If the screen-scraping works the way it's intended, you would expect WiseWindow's numbers to change a little faster than the polls, since polls are only conducted every so often, and usually include a rolling average.
I'm skeptical. Not because I don't believe that it can be done, but because I've read up on the top-of-the-line opinion mining algorithms, and they're still full of holes. Computer scientists are smart people, but they haven't absorbed the lessons that pollsters have spent almost 100 years learning.