Among the 22 ranking factors identified, social signals account for five of the six most influential factors in Google’s search results, according to a June 2012 study from Searchmetrics.
"The study showed that the most influential factors were:
Facebook shares (0.37) have the highest correlation.
Followed by number of backlinks (0.36).
Other high-ranking factors include Facebook comments (0.33).
Likes (0.3), and Tweets (0.25).
A number of factors display a negative correlation with Google rankings, including title character length (-0.04) and the position of title keywords (-0.05)".
Via Antonino Militello