Many SEO firms have tested the affect of social media interactions such as conversations on Facebook and Twitter on search result rankings. Google’s Matt Cutts confirms the use of social media as a ranking signal in this video. Back in May 2010, a video by Matt Cutts stated that Google did not use social media as a ranking component, but this has since changed. Real time search is the primary focus of this ranking signal, but Google is incorporating it into regular search results. Again, quality should be the key focus.
Twitter and Facebook do contribute to ranking as one of the score building components. Google is trying to build an understanding of reputation (of a brand’s, author’s, etc) through the interpretation of that content.