This is another one of those great arguments of causation versus correlation. Does getting social mentions directly impact your search engine ranking? Or is social a great barometer of activity on the web that generates other factors that influence ranking. Google and Facebook aren't really friends at this point – with Microsoft having access to Facebook activity, it's doubtful that Google has any insight (although they may through third parties).
I don't doubt that Google is beginning to monitor social queues to help increase the relevance of its ranking algorithms. For too long, it's purely been all about backlinks. Because of that, the SEO industry went nuts generating tons of money and tons of backlinks. Recent algorithm changes have really driven the impact of crappy backlinks down, and I believe there's much more emphasis on social mentions. I'm not the only one who thinks so, though.
TastyPlacement has done its own testing and come up with some important takeaways… the biggest of all may be to quit dragging your feet and begin using Google+ a lot more!