I smoke regularly and enjoy it very much. Unlike alcohol (which I also really enjoy), weed doesn't make you stumble or slur your speech, and you remember (mostly) everything the next day. It makes simple activities more enjoyable, and any kind of gaming *way* more enjoyable. I find it stimulates creativity, and lets you think up things you wouldn't normally (just try to write it down or record it while it's still in your head).
Like any other mind-altering substance, you shouldn't put yourself in any situation where you might cause harm to others e.g. driving, operating heavy machinery. Just use common sense.
Marijuana is the only illegal drug which is prescribed by doctors for a variety of medical conditions. And I won't even touch on the myriad uses of hemp.
I personally think it's ridiculous that cannabis is illegal. Legalize it, regulate it and tax it; and stop making criminals out of law-abiding citizens that want to enjoy the effects of a harmless natural substance.