Many SEO’s had assumed it, now Google has confirmed that they do in fact use data from social media profiles, like Facebook and Twitter as part of their ranking algorithm.
But before you run off and create 1,000 Twitter profiles and circle jerk them all in a linking / following scheme, Google has stated that just like links to your website, the quality of your profile and followers is more important than the quantity. Matt also mentions in the video below that Google is only using social media data, at least initially, as a very light influence in there ranking algorithm, which includes over 200 other factors. See the video below to get it straight from the horses mouth.
Does Google use data from social sites in ranking?
For more checkout the comprehensive article on Search Engine Land, What Social Signals Do Google & Bing Really Count?