If I offered you FB stock at $10,000, what would you say? "Too much", I hope.

If I offered you FB stock at $0.05, what would you say? Probably, "Hell, yeah, that's a bargain".

So there's a rational price that the market agrees upon, within certain boundaries. The market seems to agree that the IPO overpriced the real market value of the shares. It's a real time machine that tells us what people think the shares are worth.