To be fair, MtGox was an exchange, not a bank. My understanding is that if a standard exchange (eg, Ameritrade) went down in a similar fashion, you'd be equally screwed.
So if they screwed something up, and somehow lost all of your stock and cash, your cash would be covered by the FDIC and your stock would be lost? (Assuming they don't have some sort of supplemental insurance to cover loss of stock.)
