[CurrentB]

Unacceptable maybe, but what do you expect? No one really knows if there can be legal consequences to running an unregulated commodity exchange, and the operators of mtgox face considerable risk and charge VERY reasonable fees, which still allow them to do quite well I'm sure. It's not their fault really that they lack necessary funds to prevent such attacks, an I applaud them for just keeping data safe so far.

Anyone else is free to open up a competing exchange but it's such uncharted territory (mainly legally) that the risk outweighs the reward.

Bitcoins are in their infancy, remember. How they will ultimately be used, exchanged and valued has yet to be determined, and early adapters on all fronts are just going to have to deal with these things.

Edit: Just to add to this, during the last two attacks the guy that runs mtgox was in the bitcoin IRC channel working on the problem and giving people updates in real time. Both were fixed in a relatively timely manner (it's back up now). You really just can't ask for more from such a small operation.