Google has approximately 200 'ranking factors' in its search algorithms but a Google Webmaster video published yesterday made it clear that Twitter and Facebook shares do not currently have much of a direct impact on Google visibility. This is new, in December 2010 the same Matt Cutts confirmed that Google was using social signals at that time. Cutts seemed to express a rare bit of mild frustration yesterday as he spoke about being blocked from the signals, perhaps remembering how Twitter ended a deal in mid 2011 that allowed access to a 'special feed' of information. Search Engine Land noted back then that users would not be able to find Tweets more than a few days old, a problem that has since been solved by the Twitter friendly search engine Topsy.
Stone Temple Consulting published a good analysis of the current and future outlooks for social signals. Authorship is key, Google is obviously very interested in a system that evaluates the authority of a source in regard to a specific subject. For now, as WebPro Technologies pointed out, Google+ remains the place to establish social authority.
Cutts explained the observed relationship between Facebook Likes and Google rankings as correlation, not causation, and he went out of his way to praise the overall value of social sharing. For now, however, the best strategy seems to be to continue to build social authority to be ready for the time when Google gets the signals to move forward.