Pinterest is not exactly a "minimal Facebook integration". It is integrated with Timeline. As such, all your activity (pins, follows) are sent to Facebook for display in news feeds, and for Facebook's ad algorithms. But Nik's point is still very valid - less time spent on Facebook is less time spent looking at Facebook ads, and stream posts of brands you are following. They will have to do something to address this, maybe purchase the likes of Pinterest, or require ads on Connect sites, or something more thoughtful and strategic.