I believe a lot of bitcoin purchasing is happening in Europe and Asia. This is because when I wake up in California I notice the price sometimes jumps huge amounts overnight, I attribute this to it being daytime in Europe, and when investors invest.
I noticed the same thing. Around midnight eastern time the prices jumps. I thought it might be investors in europe and asia but it could also be that bank transfers and orders are clearing mt.gox which would be happening in the morning in Japan.