StumbleUpon may be small compared to sites like Facebook, Twitter, and MySpace, but it sends the most social media traffic around the web according to the latest numbers by StatCounter.  StumbleUpon had 43 percent of the U.S. social media traffic on January 1st, while Facebook trailed with 38 percent.

You may question yourself how it is possible a site with 12 million users to send more traffic than a site like Facebook with 600 million users? And the straight answer is because this site is specifically designed to do nothing but send traffic.

StumbleUpon formula for success is hidden in the brilliant idea to keep you away from their website. By its very nature, StumbleUpon takes you everywhere else based upon your interests, stumbling habits, friends, and what’s hot in the Internet. Using an installed Toolbar or a browser frame, users “stumble” websites, stories, videos, and pictures, not knowing where they’ll end up next.

Facebook is a tremendous traffic generation tool, but it takes a lot of time to build relationships, which will lead to more “likes” to a website’s page or more shares by visitors. Large sites with a ton of traffic are those that benefit most from Facebook’s sharing abilities.

On the contrary, SU is particularly popular amongst newer and smaller websites. It is relatively easy a new site to “go viral”, if the right mix of natural thumbs up come in.

Of course, it is completely different story what the quality of the traffic is? Whether this huge traffic comes with a high bounce rate and low conversions? Let’s face it. Bounce rate has always been very high for stumbled pages but seems it depends on the type and quality of the content as well as the site itself. Mostly images and art related stuff does well on SU.

At the end of the day, what you still have to know is where your target audience hangs out so that you can put your efforts there and thus drive relevant targeted traffic that converts (based on the desired Call to Action).