Basically, it's great for the black market. For the US, that means primarily drugs and gambling. That's why the price shot up after the Wired article about Silk Road: A whole bunch of people wanted to get Bitcoins to buy drugs online. In some countries the black market is even more important, because it's the only way to get certain necessities. The fact that bitcoins are being used as an investment vehicle right now is depressing, since the world desperately needs a form of digital cash.