My conspricay theory, based on no facts or special knowledge but sheer speculation is this -- gox wasn't holding as many bitcoins as they should have been and were worried that they would have to buy bitcoins at $200+ each to fund withdrawls. (maybe they were planning to buy them when the rally ended but it never did and they got in dfeeper and deeper) So they staged a problem, crashed the price, bought up all the bitcoins they needed, and then resumed business as usual. They hope hte volatility will actually bring more speculators, becuase the more the market moves, the more opportunities for things like day trading there are, and nohitng makes gox more money than people who trade a lot.