A question I get a lot is “Why is the price on X exchange so different than the price at Y exchange?” Or, “Can you buy me Bitcoin at X, exchange? They are so cheap there now.”
Today’s price differences are an extreme example of the differences of exchange pricing. At Mt. Gox you can buy Bitcoin at US$275. But here’s the thing- they are not letting you get your Bitcoin out!
The price difference is probably caused by people not being able to move their Bitcoin, and believing that trading it for cash is a safer option- assuming that Mt.Gox can’t steal their cash. So, you have thousands of people selling the asset, and only a few people buying = lower prices as people dump their assets for cash.
In an efficient market – the ability to arbitrage between exchanges will keep the prices closer. But in the current Gox situation, neither Bitcoin or cash are able to move out, and there’s fear that it could collapse. This creates some extreme pricing.
You may be tempted to put cash into Gox to buy up the cheap bitcoin and then wait for them to resume transfers (however long that may take- it could be today, next week, or never)… You must make your own decision on that. I wouldn’t risk the permanent loss of capital on such a risky bet.