I just noticed that google is giving more weight to Twitter (the backlinks you may get from twitter) since Panda. So if your site gets tons of tweets you're likely to rank.
But Twitter is a geeky platform that doesn't give the real picture. Facebook's likes are much closer to it than tweets.
I heard Google doesn't have access to those likes, but that doesn't mean they should over-rely on twitter...
(If only someone could kill Panda!)