It was China driving the rally above 400 last might. Every move the Chinese exchanges made was followed by the Bitstamp, except Bitstamp lagged behind by 20 ot 30 dollars. The crash afterwards was at bedtime for China, and was probably caused by Chinese traders profit taking before sleep. If there's another BOOM the Chinese will cause it.
China at this point is the most important market for Bitcoin. Most likely all bull runs and rallies will be due to China. I hope we will stay steady at over $400 for a month at least.