The world economy has never seen anything quite like Facebook before -- that's why it's so exciting. They could become Google/Netflix/LinkedIn/Zynga combined. I'm not saying they will, but they've got the prerequisites: 1 billion active users.
Or they could become the next AOL/Myspace/Friendster/Ning combined... (IMNSHO, that's at least as likely as the former).
There is a fairly strong chance they will own an enormous % of market share of ALL online and mobile display advertising in the near future.
As Facebook figures out more ways to be a more pervasive force in people's lives, they'll have the ability to multiply the revenue they receive on a per-user basis.
They certainly can't expand the user pool by that much, which means that they need to find a way to monetize their existing users more effectively. I think that Facebook can certainly make more/user than they currently are. $5, maybe $10/user is possible. But $100? I don't think so.
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?
http://venturebeat.com/2009/03/19/the-worlds-most-lucrative-...
That doesn't sound to me like a "proven revenue model" to support a $104B company with exponential growth.
Certainly, most future growth will come from extracting more cash from the pool of users (or people selling to them), not growing the pool.