Virtual goods. It is a proven revenue model for social networks.
http://venturebeat.com/2009/03/19/the-worlds-most-lucrative-...
The link is from 2009, the title is "The world's most lucrative social network? China's Tencent beats $1 billion revenue mark".
That doesn't sound to me like a "proven revenue model" to support a $104B company with exponential growth.
So then are advertisers willing to increase their FB advertising budgets exponentially? Does FB have something coming down the pike on a regular basis to make that happen?