I don't smoke it but am an advocate of legalizing it. The benefits on society are big (and I don't mean everyone walking around stoned will result in a "calmer" and more "laid back" American culture) and the money (a tax) from it could be tremendous.
Checkout this article from the Prometheus Institutes's blog. It lays out exactly what we could get and then what we could do with over $10 billion in federal funds. Not bad.
There is a lot of history on the public perception of marijuana and how it has come to be looked at so negatively. Politicians who once did it in college poo-poo it, teachers who preach against it in the classroom use occasionally and a culture that fears it spends billions each year on stopping its impact on our lives (the whole War on Drugs is part of that really successful Republican "war on nouns" platform that seems to always end in defeat by obscurity -- "War on Poverty" was a real gem from the Regan-Bush days). Regardless, its time we cast away our old-time assumptions about it, grow up and let it be.
When you can profit $10 billion from it (not to mention the profit from hemp production!) can we really pass it up?