On a side note, the fact that bank runs are rational decisions and that no FDIC-style agency exists to change the incentives seems bad for cryptocurrency in general.
(Possible responses include both "the traditional financial system and fiat currency is actually pretty good" and "someone should run a reliable FDIC equivalent as a business for new exchanges and new coins".)
Isn't a bank run only an issue if the bank is using a fractional reserve? Cryptocurrency exchanges aren't banks; they're not supposed to keep a fractional reserve. If everyone suddenly demands all their coins at once, the exchange should have no trouble complying with that.
The only problem is that there's no way to know for sure whether an exchange is running on a fractional reserve or not.
They claim that they don't. If they do, that is a serious problem. Some of the exchanges have, but there is no evidence i'm aware of that points to any of the current major exchanges running a fractional reserve.
The issue is that once there is evidence there is a bank run. Mt Gox wasn't supposed to, but they did. And there are others out there that I hear rumours about having 5 or 10% of their reserves stolen from hot wallets. Sure it's fine if there is never a run, but it's worth pointing out that this is a real threat vector.
