Recently (Dec 2010) Search Engine 'Guru' Danny Sullivan interviewed representatives from Google an Bing as to whether or not (and how) social media influences search engine results. For the first time representatives confirmed that social media involvement, specificallyy Facebook and Twitter, are indeed a 'signal' they use to determine ranking relevancy.

The full interview can be read on the SearchEngineLand website but in it Google and Bing confirm they look at retweets and links referenced in Twitter. Both confirmed that public information on Facebook (ie Fan Pages, links shared to 'Everyone') are also tracked.

Clearly social media engagement is important to anyone serious about search engine marketing efforts. If you produce meaningful, engaging content and you want to recieve the full benefits of this you want to be sure you are exploring social media optimization to its fullest.