StumpleUpon reigns supreme over social media trafficking.
According to StatCounter, StumbleUpon has passed Facebook and now refers more than half of all social media traffic in the U.S. as of August 2011.
Facebook has fallen to second place, referring around 38 percent of U.S. social traffic. Other sites such as Twitter, Reddit, YouTube, MySpace and Digg refer fewer than 4 percent each.
Although this study may not be surprising when taking into consideration that StumbleUpon is created for users to stumble onto sites around the web, the surprising aspect is the difference between each sites user base. StumbleUpon has a much smaller user base at 12 million compared to Facebook's 750 million.
Additionally, it will be interesting to see if StumbleUpon's recently released explore feature, which makes it easier for users to stumble upon desired topics, will lead to an even higher referral rate in the coming months.