There's no way the federal government could enforce this on the streets. Maybe in the books, but with local and state PD ignoring recreational use, the typical user has little to fear in terms of legal recourse.
I expect there will be a large "spike" in use at first, which will decline to a high to moderate level that will last a couple years, followed by a drop below the current levels.
It's hard to explain why, but once weed becomes as common as alcohol, the bubbles of people within which smoking daily and such is an acceptable lifestyle and even an identity, will dissolve and smoking daily will be more akin to alcoholism. Considering most people who want to smoke weed now, do, regardless of it illegality, once the churn of new users is done experimenting the "f*%#-the-police" appeal will be lost, the "I was too scared to try it before because I could get arrested, but now Im not" group will not be enough to outweigh it, and the "its okay to smoke weed every day cause everyone who knows I do does too or can't talk about it" ideology dissolves, I expect the numbers should drop below the current [actual] average, if not that then very close to the current average (which would still be "below" since they'll the current average will be under-represented in comparison).