A while ago Rand Fishkin of SEOMoz.org released the results of a study his company did that analyzed the impact of social media signals on search engine rankings. You can find the study here
Basically it said that the search engines pay a lot of attention to social media signals and Facebook shares are the most important signal. I wanted to test this idea myself so I brought an exact match domain name for a two word phrase that is not very competitive. I submitted it to Google, Yahoo, and Bing. Within a week it was in the index of all three, but it did not show up in the top 100 results.
Then I shared a link from my own facebook account. Within 24 hours the site ranked #14 in Google and #12 in Yahoo and Bing for its core term. I got two friends to share links to it and again in 24 hours it move up to #6 in Google and #4 in Yahoo and Bing.
I think this proves that Facebook shares are a VERY BIG DEAL in SEO. Has anybody else seen this kind of result? There is no way I would have gotten the same result from a few links from PR3 sites.