Looking at what's going on with the price discrepancy between Mt. Gox and other exchanges, I can't help but think this demonstrates a bad incentive for exchanges.
Right now, anyone able to get funds onto Gox can make a ridiculous profit by arbitraging. Trouble is, most people can't withdraw BTC, so the play seems risky. But who's best positioned to get funds onto Gox accounts? Gox, of course. And who has most reason to trust Gox to allow BTC withdrawals? Gox again.
I don't know what's going on at Mt Gox. Right now, however, they have a financial incentive to not fix their problems, if they're buying BTC themselves and selling elsewhere. The same incentive exists, in principle, for any exchange. Run your service to the ground, get people good and scared and use your house edge to buy their BTC on the cheap. Even if this isn't what Gox are doing now, as long as the incentive is there, someone will do it eventually.
I'm not sure how this can be solved, other than not using exchanges.
You solve it like you would any other business, you don't give money to incompetent fools who show you time and time again that they cannot be trusted.
