But some states have laws regarding driving under the influence on Marijuana, in which you can be charged for being high. I also remember hearing about laws against public influence of marijuana as well but I don't know much about that.

But for the most part, useage is the lowest of all crimes. You see, posession means a chance that its for distribution while usage ensures it is not.. so a cop will have to be a pretty big dick to bust anyone for usage. Cultivaters and Dealers, you just gotta be smart and watch your ass to avoid gettin pinched.