I heard about this yesterday - Web Traffic Measurement Company Quantcast Raises $20M More:

"…The round was led by the Founders Fund and included Polaris Venture Partners. It follows $6 million in previous funding from Founders Fund, Revolution Ventures, Allen & Co., and the company’s founders…"

We have a couple members of Quantcast on Social Media and Community Committee at the Web Analytics Association, which I Direct, and tomorrow, at the Digital Media Measurement & Pricing Summit which I'm attending, Adam Gerber, Chief Marketing Officer, QUANTCAST will also be speaking - so I'll reach out to him.