I am extremely shocked that MtGox does not have one simple security feature that I have asked for more than a year ago (when I still was willing to do business with MtGox):

Allow users to lock withdrawals to a single bitcoin address

And allow changes only with a signed message (PGP or a signed message from the current address) EDIT: or (per another suggestion in this thread) after waiting out a lockout period long enough for the real account owner to contest a request initiated by a hacker

This would virtually eliminate ALL the theft without ANY groundbreaking innovation (other than a small modicum of easily acquired common sense)

There might still be theft if the person gets their wallet stolen, but that's a burden that sits squarely on the user, and moves the risk completely out of MtGox's sphere of concern.