Jakob Nielsen: Email Beats Social Media in Business Value

The analytics company Monetate analyzed 100,000,000 visits to a range of e-commerce sites.Conversion rates differed dramatically, depending on where users came from:

Traffic Source   Conversion Rate Email 3.9% Google 2.4% Facebook 0.5% As I have said before, our user studies show that people use social media to be, uhm, social: to connect with family and friends, and not so much to connect with companies. This doesn't mean that you should avoid social media, just that you should focus your budget on SEO and email, since they offer much better returns.

Jakob Nielsen: Email Beats Social Media in Business Value