This guy's done some interesting math on MtGox's supposed loss of bitcoins. It's interesting that the quantities that are missing are so large, even spread out over MtGox's existance. And depending on how you do the math, there weren't even enough coins in existance for a while to sustain losses that are being reported. Read for yourself: http://letstalkbitcoin.com/somethings-not-right-at-gox/