There is no doubt that a strong social media strategy is important to a successful SEO campaign.
Actually, Google knows very well that the social world exists. They added real-time results to the SERPs quite some time back. Basically, if you tweet about your latest blog post or about a brand new product being released and someone puts in a query looking for it – they will get it in the organic search results.
Google includes Facebook fan pages in their real-time searches and they also index Twitter updates. This means that Twitter and Facebook updates are important parts of a social media strategy and can be optimized much like content is optimized.
And even if the backlinks you get from many of these sources are no follow links, you can still generate much referral traffic and even no follow links can help improve your rankings.
Via Antonino Militello, Peter Rees