After the Mt. Gox thing the bitcoin course is going back up again. My initial response was “this is a Mt. Gox problem, not a bitcoin problem” and I think this seems to be the general opinion right now.
But then it looked like the most likely reason for the disappearance of the money is that some insider at Mt. Gox just ran away with it. And the more you think about it, the more you realize how easy this is. Let’s say you are an admin at a company which has a lot of bitcoins. One day you book a vacation to some Caribbean island, and the day before you leave you copy the private keys of all the big bitcoin wallets that the company has onto a thumb drive. As soon as you’re out of the country you use those private keys to transfer all of the company’s money to your account. You’re rich, and it’s not easy to see how that could have been prevented.