One word – traffic. Shareaholic posted a study of referral traffic in January 2012 from more than 200,000 publishers with a combined total of over 260 million unique monthly visitors. The top five social referrers were Facebook, StumbleUpon, Google, Twitter, and Pinterest. Note that Google in this reference is only for referral traffic from products, not organic search or AdWords. This means that Pinterest beat YouTube, Reddit, Google+, LinkedIn, and Myspace combined for referral traffic.