I'm somewhat confident right now that this is a big technical snafu based on old bugs that MtGox hasn't bothered fixing in a while (such as the known coinbase bug and the known duplicate spend bug), but which snowballed now that many people have panicked (like I have) and tried to withdraw.
um.... yeah.... that would be panic that never in a million billion years would have occurred with the teeniest tiniest amount of transparency or explanation as to what was actually going on.... an explanation which we continue to wait for. Perhaps the secrecy was to avoid looking incompetent and thereby losing the trust of the customers, but the secrecy itself has had the effect of.... yep, you guessed it. Technical incompetence + customer service incompetence = sinking ship.