Point to another public company that has a P/E ratio as high Facebook that is missing earnings estimates. Nobody is claiming the company is going to fall apart tomorrow, but if growth is slowing already then they certainly aren't worth $100BB, or anywhere close.
I don't know how bad this really is, and we are still in a shaky economic climate. But if we assume that the information being reported is true, this is pretty bad. As the article suggests, they're applying some "quick fixes" to crank up the ad spends. Is that the best they can do?