I just stumbled upon this site and haven't had a lot of time to verify how well it works, but if it does what it says it will this site might one of the best uses of the Twitter-stream that I have seen to date.
Basically, it scours Twitter looking for movie titles and then attempts to evaluate whether or not someone wrote a positive or negative review of the movie. After that it aggregates the results into a list. I will definitely be using this before I see my next movie!
Is this kind of application useful to you?
What other online apps do you think are making good use of social media data?