Well, while I don't look forward to the inevitable, if possibly slight, increase of people smoking weed, after a few rather interesting discussions with my father, maybe nation-wide legalization of Marijuana would not only be good for the country, but the economy as well.
Think of it like this: If Marijuana is legalized, it would have to be treated the same as Alcohol, Tobacco and Firearms. Yes, now the ATF would be the ATFM. Even if it IS legalized, it would have to be regulated. Laws would probably be put in place, such as no smoking while driving, or while operating heavy machinery.
Not only that, but it would handily disarm (not sure if that is the right term for it, but I can't think of a better word for it at the moment) drug cartels working in the US that center their trade around Marijuana, and those that grow it in the United States itself, may end up becoming legitimate farmers of the stuff, and earn a legal, possibly government paycheck for it.
To help the economy, the government itself could always tax it, and rather heavily too. Looking at it from the outside in, nation-wide legalization may actually be just what the US needs.