Forty-two percent of 12- to 17-year olds can buy marijuana in a day or less; 23 percent in an hour or less. Compared to last year, this is a 35 percent increase in teens who can buy marijuana in an hour or less (23 vs. 17 percent) and a 14 percent increase in teens who can buy marijuana in a day or less (42 vs. 37 percent). From 2007 to 2008 this represents an increase of 1.4 million teens who can buy marijuana in an hour or less (5.8 vs. 4.4 million), and an increase of 1.1 million teens who can buy marijuana in a day or less (10.6 vs. 9.5 million).Half of 16- and 17-year olds say that among their age group smoking marijuana is more common than smoking cigarettes.Marijuana continues to be easier to buy than beer: 23 percent of teens find it easiest to buy compared to 15 percent who find beer easiest to buy.
I found the link to that report in a New Scientist piece arguing that prohibition is ineffective and makes the world a far more dangerous and ugly place. Prohibitionists need to disprove that if they are to be taken seriously.