Early onset cannabis use and psychosocial adjustment in young adults - FERGUSSON - 2006 - Addiction - Wiley Online Library
This is a great article from the Journal of Addiction. It attempts to break out the "were gonna smoke it anyway" crowd from the real data. Studies psycological effects, gateway effects, and crime instances. If you have a college library they should be able to access it for free and pull up this issue. The link is just the abstract.
Needless. In a strange move, US Attorny General Eric Holder wrote that the Federal Government would continue to enforce the law and that this would be a stumbling block to cali - washington relations.
I will note the reason the drinking age is 21 and not 18 in all states is because the federal government. They recommended 21 but couldn't enforce it as a matter of states rights. So they just cut off all DOT roadwork funding for all states that didn't agree with this recommendation. It would not surprise me if Prop 19 passes then some aspect of this give and take will be applied. I don't think the federal legislature is ready to legalize yet.