The problem is that Facebook's primary asset is users. They're making money off of them(approximately $1/user in profit and $3.5 in revenue), but it's not clear if they can make exponentially more per user.
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.
Hard to imagine exponential growth in what either users or advertisers are willing to pay. An analogy to FB as a user service might be, say, MMORPGs like WoW. They seem to exhibit early exponential growth due to peer pressure. Yet they are never priced more than $10 - $15/mo. Often they start out as a subscription service and then move to free-to-play.
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?
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.