Although I am new to the community and been only a Bitcoin follower and trader for a week now I have analyzed and studied many articles and papers about Bitcoin. I follow the market closely and I have ready dozens of articles, threads, and comments relating to the Mt. Gox incident. As a web developer and using my logic my personal opinion is that Mt. Gox fucked up big time when we look at their website security and how they are handling this. Although we can't verify if the account with the 500k Bitcoins really existed or not does not matter when you look at the dispute between Mt. Gox and Kevin.
So far Kevin has done nothing wrong, just like anyone would do in this situation and tried to buy as many Bitcoins as possible for .01 cents and than tried to withdraw them as fast as possible before the market and Mt. Gox crashed. If I had 3000 dollars on my Mt. Gox account I would have done the same freaking thing. Some people argue that it's impossible that Kevin was able to place a bid after the hacking started as the website was to laggy or down. This is different for every PC and totally depends on the connection, DNS, location, server, etc. A website may be down or slower for someone than for someone else.
If is telling the truth I believe that he should be allowed to keep the Bitcoins he legally bought even if the account with the 500k Bitcoins was hacked. In a real exchange the same thing would happen. An exchange cant revert hours of trades back just because one account got hacked. No matter how much money there is on it. If Mt. Gox reverts all the traders because of this than I want to see them do the same thing when my account gets hacked and my 10 Bitcoins get sold.