It'll be interesting when marijuana is legal to see how many people will keep their jobs. I work at a place where everyone smokes and we speak about it freely in front of the manager. We're not required to take drug tests, but I can imagine if something like this were to happen we'd all be screwed. And what I hate about this is that drinking is completely fine.
What I think is even more interesting is happening now. As marijuana is legalized in certain states and not all it seems to be setting up a confrontation. What if thenewgreen has been smoking legally in Colorado the week before when he returned to his job in Montana for example? Or potentially even more difficult, for federal security clearance you generally have to be drug free for some amount of time before taking the job, well what if you come from a state where marijuana is perfectly legal? Does that prohibition still apply?
All these consequences of disjointed state/federal laws will eventually lead to a national law legalizing it. It will happen in the next 10 years, but then they likely said that 10 years ago, right?
I think it'll take longer than 10 years, but things are definitely progressing. I think it'll be difficult for the more conservative states to loosen up on it. But who knows? at that point the federal law may have already legalized it.