Approximately how many payment transactions occur globally each day?

I think this would be very difficult to answer with any reasonable degree of accuracy. Forget the world, getting such information about Chinese market which is huge (or India) for that matter would be almost impossible, and without these two economies, very difficult to come up with a number.

Having said that, I would love to see someone do the "Lets assume there are X many people in the world ..." scenario and extrapolate an answer.