Mathew Ingram on the Facebook valuation:

In reality, of course, every economist knows that things are only worth what people will pay for them, and since no one has actually paid $33 billion for Facebook, we shouldn’t really say that it is worth that much, or that Zuckerberg is worth $6.9 billion. But then, no one has paid $165 billion for Google either.

Very true, but what I really take issue with is saying that Zuckerberg is worth $7 billion because of it – you are only worth what you have in liquid assets (obviously a matter of opinion). Facebook is anything but liquid.