I've always wondered this question myself. I have trouble believing some estimates (20-30 million people) because I don't agree with methods used to determine them. I can't see a poll being very effective because you're going to get a lot of lies if all you are doing is asking a few questions and moving on (i.e. people saying they don't smoke when they do or saying they do smoke when they don't [to fit in, or seem cool or just to lie.]) I don't really see arrest records as being anything more than a starting number because yeah a lot of people get busted with cannabis but just imagine how many people DON'T get caught. I know most estimates claim that half if not more of the US has tried pot at some point in time. It just seems to me that the number of active users are higher because almost anywhere I go I will find a fair number of pot heads and it isn't solely in my own social circle/class.