It is worth mentioning that since Mt. Gox has the highest confidence in the exchanges market, it consistently trades 10 - 20% higher than other exchanges almost all the time (unless major market movements propagate downwards from Gox, in which case it would be trading lower before everyone else, but that reaction time is measured in minutes or seconds for cost correction across exchanges) so if you want, you can buy more "risky" bitcoins from less popular exchanges, move them into Gox, and sell them in Gox, doing so successfully means you took the "risk" on a less popular exchange and get the difference in moving the money into a more confident market.

Just as an example, bitstamp is trading at $75 while Mt. Gox is at $120 right now. So if I were to buy bitstamp coins, assuming no major market movements rapidly drove Gox down (which would also drive bitstamp down too) you could move BTC from stamp to Gox and pocket a profit of around $45 per coin by taking the risks involved.