Things (shares, companies, objects, currencies, oppurtunities, gold) are worth what people will pay for them. That's it. There is no objective "value" other than that.
A company is worth the expected net present value of all future dividend payments. If a company is both unsexy and well-managed, you may be able to buy its stock at a very good price, and then collect a fat profit of the dividends.
That's their price, but price and worth are different things during periods of irrationality. I think it's pretty clear that people are projecting what Facebook will be worth when it hits a Microsoft 00s style plateau, and deciding on what the price should be now to reflect that.
After all, Yahoo's market cap peaked at $152 billion and Google's IPO was 1/6th today's price.
