Three main issues....
1. Increased DUIs. Not as big of an increase as you might have expected, but there has been an increase tied to high driving. I drive a lot and ANYTHING that contributes to distracted driving (texting, pot, pain meds, booze, putting on makeup while driving on the highway) pisses me off. When you are driving - DRIVE.
2. Despite what the Gov said in the article Howie quoted above, there has been an increase in teen pot usage, and a big increase in pot related teen problems. I have several friends who teach in local high schools and Jr High Schools. At the high school my kids all attended the suspension/expulsion rate this year is more than triple the normal rate and the root cause is underage pot usage (suspensions) and pot selling (expulsions). There are also increased behavioral problems since teens just are not good with decision making and ingesting a lot of very strong pot is not a good contributing factor.
3. Increased pot addictions. I know this is a 'controversial' issue, but I know people who are/have been addicted to pot. It might be more a psychological addiction than a physical one, but it is very real.
I do think that the issues overall are actually less than a lot of people anticipated, but particularly the problems in the Jr High and HS level are worrisome.