What I haven't seen anyone say these past two months of growth is that the value of Bitcoins must necessarily increase before it becomes a real currency. In order for people to use and exchange Bitcoins, they must buy them. This will increase the value. If, at some point, Bitcoin becomes a mainstream currency, this kind of extreme growth must happen. In fact, we should expect that Bitcoins will be worth orders of magnitude more than they are now if they come to represent any significant fraction of the world economy. Today, Bitcoins are only worth about $1.3 billion, which is tiny. This particular price hike might be a bubble, but it could also be the start of a real Bitcoin economy.