Late last year there was a lot of talk about how negative reviews were boosting one sunglass sellers search engine rankings. This was because the Google algorithm factored in the total number of reviews for a company and didn’t place weight on whether they were good or bad. After a NY Times article about that particular seller Google changed their algorithm to factor in user sentiment. Essentially slightly burying merchants that get poor reviews.
Way back in 2007 Google presented an academic paper at a University of Colorado conference title “LargeScale Sentiment Analysis for News and Blogs (System Demonstration).” That paper laid out the general ideas of how sentiment works within the Google algo. Here’s a link to that paper: http://googleblog.blogspot.com/2010/12/being-bad-to-your-customers-is-bad-for.html