Mahalanobis has a post up with a collection of informative graphs on the usage of various recreational drugs around the world, along with links to interesting posts elsewhere on the subject.
What's interesting about the graphs from my point of view is just how little difference drug policy seems to make to consumption: the USA is at the head of the pack for almost every drug shown, other than heroin, and even the Colombians appear to sport fewer cocaine users per head in their ranks than does Britain or the land of the free, despite the fact that they're the ones who grow the stuff. One would think that people in poor countries would be heftier consumers of drugs, what with the more serious challenges of survival they face on a daily basis and the laxer policing they have to put up with, but this assumption isn't borne out either, not even for marijuana usage.
The one pattern which does stand out to the eye is that "Les Anglo-Saxons" - i.e, Britain, America, Australia and to a lesser extent, Canada - seem to have an unparalleled appetite for mind-altering substances in comparison to the rest of the wealthy countries, with the French standing out for their general restraint (except when it comes to marijuana). I cannot think of any plausible explanation for the first pattern other than that there appears to be an ongoing convergence towards American cultural norms throughout the rich English-speaking world, and I'm not even going to attempt to explain the French exception.
PS: On a related note, I've just discovered Jonathan Rauch's satirical take on the whole "War on Drugs" nonsense, and I think his piece nails the problem with the effort square on the head - not even a police state would suffice to abolish the laws of supply and demand, which apply as much to recreational drugs as to any other goods on the market. If drug use is a problem - and I am unconvinced that is in itself as problematic as usually claimed - then the answer is to change the cultural attitudes which create demand, not to turn the lives of Colombians and Afghans upside down in a futile bid to eliminate supply.