http://www.bitcoincharts.com http://www.bitcoincharts.com lists the daily trading volume of various exchanges. I think the numbers for Mt. Gox represent the vol

http://www.bitcoincharts.com http://www.bitcoincharts.com lists the daily trading volume of various exchanges. I think the numbers for Mt. Gox represent the volume before things went sour, so based on that, Mt. Gox sees almost 30 times the volume of the next largest exchange.