JR, I doubt it's going to come as much of a surprise when I say I have, but I'll say that the only real affect it's had on my writing is the knowledge of what it's like to do those drugs. I can't say there was any mystical enlightenment. I did write a short piece while I was high on mushrooms once, and while it was riotously hilarious to go back and read later, it was due mostly to the varying letter sizes and curiously placed punctuation. I've known other writers who have made claims to being enlightened by drugs, as well as artists and musicians, but it's always just another -head justifying his next fix. From what I experienced and from what I've heard said by others who do claim some magical journey, hallucinogens only have that kind of effect on douchey little twats who like The Doors a too much, and even then it sounds mostly like twaddle. Those people are going to find anything deep if someone tells them it's deep.
Now, I'm not saying it's never happened that people's creativity has been tapped while high, I know it has, but it's not a substitute for talent and work. Plus, regardless of how responsible you are as a drug user, any time you make it necessary, you make yourself an addict. Drugs can certainly heighten your awareness, but they call them hallucinogens for a reason...they make you see shit that isn't there.
I exclude alcohol and marijuana from all of this, just because the kind of intoxication with those is fairly mild and I've used both to help me focus and open my brain a little. In those cases, it's the mellowness offered and not so much the consciousness-awakening that is the help. Honestly, though, the things that help me write most are coffee and cigarettes. A little music playing in the background doesn't hurt.
Aaron Sorkin is a really good writer who uses drugs. To my knowledge, he doesn't use drugs to write. A whole lot of writers are like that...in fact, I think you'd be hard-pressed to find a writer worth reading who doesn't indulge in something, and I guess that's the other side of the coin. Many people working in the entertainment arts have a tendency toward getting their heads bent in some way or another, it seems to be the nature of the beast, but most, I think, understand there's a big difference between using drugs and using drugs at work. Drugs are fun, but for every writer who makes drug use work, there are a dozen and more that become cracked-out paranoiac junkies.