Sentiment analysis
From ScribbleWiki: Analysis of Social Media
Class meetings
The Sep 4 lecture of the Analysis of Social Media course included an overview of this area.
Sentiment-Related Competitions
The TREC Blog Track ran a opinion detection task in 2006 and 2007.
Research in Sentiment, Opinions and Subjectivity
Research in Sentiment, Opinions and Subjectivity : Papers, people, and resources