CainIV - 6:10 am on Dec 11, 2012 (gmt 0)

A correlation study at SEOMoz shown a statistically significant connection between social sharing and mentions and rankings across a range of niches.

That being said, the study also appropriately noted that it was the chicken or egg phenomenon - were the sites more socially shared because they were inherently higher quality and more relevant, or were they socially shared, and because of that, ultimately received higher scores in search.

One thing is for sure - social media helps to spread high quality content both on the website and off, which can lead to better performance.