I used to smoke quite a bit when I was in high school and throughout undergrad and post-grad. It was a good way to wind down after a long day of classes and studying. The best part was that I could be totally functional the next day because of the lack of hangover.
I stopped because it just became something that I did less and less, and then I just stopped. Also, the friends that I was spending more time with didn't smoke. I guess I just found other ways to be entertained.
My wife was never into it, I think we smoked a joint once together..... she got all paranoid, it was quite funny.

That's probably another reason I don't anymore.
However, if I was at someone's house or at a concert or a party, and a joint was going, I wouldn't hesitate to pull from it a little if it was offered to me.
I hope it gets legalized in my lifetime......