As if there was ever any doubt that the “pin” is winning, a new report from Experian says Pinterest is now the third most popular social network in the U.S., based on number of visits, surpassed only by Facebook and Twitter.

Experian’s “2012 Digital Marketer: Benchmark and Trend Report” says social networking has reached new highs, with 91 percent of adults using social media regularly as well as 15 percent of all U.S. Internet visits dedicated to social media sites in December 2011. But the landscape of social media has changed greatly in the past year. Pinterest, for example, is virtually coming out of nowhere to now having President Obama “pinning” on the network.

Pinterest surprised many last December when it was revealed as a top 10 social network. The new Experian report says Pinterest’s traffic surged 50 percent between February and January of this year, which is growth that’s stunning in itself. That surge has allowed the site to overtake services like Tumblr, LinkedIn, and Google+ for what Experian says is the third highest number of visits in February. Experian’s report didn’t go into that much detail, but we contacted the firm and they provided the following brand-new data for March, showing Pinterest at a clear no. 3 position for U.S.-based visits:

Adding to the good news, analytics firm comScore also said recently that Pinterest attracted 17.8 million unique visitors in February from the U.S. alone. In terms of engagement, Pinterest is winning as well, with users spending an average of 89 minutes per month on site. However, the social network still lags behind Facebook, which has users spending an average of 405 minutes per month on its site.

And not only is it fun for users, it’s also a killer tool for marketers. (VentureBeat even has a Pinterest board.)

Pinterest is so popular as of late that it even has tons of clone sites trying to take its concept of pinning photos and products by adding a twist. There are travel-focused sites like Trippy, Wanderfly, and Gtrot. There’s several dude-focused sites like Mantersting, Gentlemint, and even Snatchly, a Pinterest for Porn.