I don't know quite how common knowledge this is, but I think it's fairly well known that Facebook are piloting external ad sales outside of facebook.com, partic

I don't know quite how common knowledge this is, but I think it's fairly well known that Facebook are piloting external ad sales outside of facebook.com, particularly on mobile[1][2][3]. So Facebook already uses external ad networks, and as they're buying up inventory from other providers some Facebook specific data is getting passed between various companies. The data isn't being 'sold' as such, but it is being tracked. Currently this is mainly focused around getting Facebook app developers to advertise their apps through resold inventory [1]: http://www.adexchanger.com/social-media/facebook-goes-wide-with-mobile-ads-for-app-developers/ http://www.adexchanger.com/social-media/facebook-goes-wide-w... [2]: http://www.businessinsider.com/facebook-is-testing-a-product-that-will-revolutionize-mobile-for-users-and-startups-2012-10 http://www.businessinsider.com/facebook-is-testing-a-product... [3]: http://www.adexchanger.com/social-media/facebook-tests-mobile-ad-network/ http://www.adexchanger.com/social-media/facebook-tests-mobil...