I suspect to some extent it is if the main value is measured in terms of how much of the economy can it directly influence and perhaps capture... If Facebook's model is to become another tool that makes the connections between seller and buyer easier and more likely I can't imagine why the IPO was valued so high. User growth may indeed be another billion in the next few years, but that will mostly come from segments of the world economy that total less than 10% of the economic consumption of the first billion.
They are in need of a model or two that will allow them to justify their valuation - my guess is they won't manage it, but at least I'm not a knowing investor (the funds we have money in may be in to some extent - that would be their own folly).
In the meantime I expect more than a few negative articles like this one in the Atlantic along with more than a few rumors and huge amounts of speculation.