A whopping $35 million for RockYou's social-network apps

That rumor of a $400 million valuation might not be too far off base: social-media application powerhouse RockYou announced Monday that it has raised $35 million in Series C venture capital.

The round was led by venture firm DCM, with contributions from several private investors. Previous RockYou investors include Lightspeed Venture Partners, Partech International, and Sequoia Capital.

It's the kind of money that may raise a few eyebrows, considering many believe the social-application space doesn't offer a proven business model yet. RockYou is responsible for a number of popular applications--SuperWall, Vampires, Likeness, X Me--on Facebook and several OpenSocial-compatible platforms (MySpace, Hi5, Friendster, Bebo, and Orkut), as well as an ad network. The company has already done marketing campaigns for clients like Paramount, New Line Cinema, Sony, Microsoft, and CBS, and claims to have 87.5 million monthly unique visitors with 2.7 billion page views.

Along with Slide, RockYou is one of the biggest companies in the social-network application development space. And with the $35 million, RockYou plans to work on "additional tools and services" to further improve its advertising platform for brands and marketing campaigns that want to jump on the social-application craze.

"DCM believes that RockYou will be the catalyst of this new global ecosystem that delivers next-generation advertisements through its innovative advertising network and social applications," DCM co-founder and general partner David Chao said in a release. "With the current momentum, RockYou is positioned to become a top-10 Internet property in the world in the near future."

Disclosure: CBS, one of RockYou's past clients, has agreed to acquire CNET Networks, publisher of News.com. The deal is expected to close in the third quarter.