http://www.ama-assn.org/amednews/2011/06/06/hlsb0607.htm
This was released 2 weeks ago, very current and provides details.
Who: Probably poorer people, which is ironic when you consider the price of it
What: Smoking can consist of cigarettes and cigars, drugs like marijuana, synthetic drugs, and tobacco products like chewing tobacco
When: Smoking is present throughout history, laws have recently begun cutting back on marketing
Where: Pretty much everywhere in the world
Why: Peer pressure, marketing, the "I'll just do it once" mentality