TweetFeel
TweetFeel gathers recent tweets about whatever search term the user has entered, and then evaluates those tweets for positive and negative feelings. Tweets including the search term flow down the screen as they are counted into positive or negative buckets.
The site offers an overall percentage number to indicate whether the majority of results are positive or negative.
Here is an example result. Judge for yourself!

Traffic rankings are sourced from multiple sources, if available, for the Twitter application. This includes Alexa, and Compete rankings.
July 13th, 2009 at 4:26 PM
TweetFeel: TweetFeel gathers recent tweets about whatever search term the user has entered, and then evaluates t.. http://tinyurl.com/mdz73z
July 13th, 2009 at 5:18 PM
Twitter Apps: TweetFeel http://tinyurl.com/mdz73z