Basically I would be happy if you get my account back up and it has my old balance, plus BTC I deposited since then. (And for folks who deposited alt coins, should have their alt coins). Since we deposit to static addresses, even the old backup should still have the deposit add'ys, and those can be matched with public blockchain data. Thus the only loss is whatever we made or lost trading since last backup. And given the low volume on the site, it's guaranteed to be pretty low numbers provided we don't lose deposits.

Yes, we can't trust our private keys to other folks. Yet we do, b/c we want to buy and sell alt coins and we're too lazy to join Bitcoin WoT, or to deal directly.