I don't know if you are familiar with Brazillian Jiu Jitsu or Submission Grappling but there are some high level people out there that swear marijuana improves their grappling ability. Eddie Bravo and Joe Rogan both smoke a lot of dope and say it helps with their grappling. Eddie Bravo is a highly respected teacher of Submission Grappling. Joe Rogan (yes the guy from Fear Factor) commentates UFC and last I recall held a brown belt in BJJ.
I know Nick Diaz was smoking a lot of pot while being a fierce competitor in the UFC and had a victory against Takanori Gomi overturned after testing positive for marijuana in PrideFC. They claimed it numbed him to the pain of Gomi's punches or some shit, even though it is highly unlikely the positive result indicated he smoked before the fight. If he did it would definately be a disadvantage in MMA anyway.
I used to be pretty into BJJ and grappling as well as boxing and the like. Mostly self taught with DVD's and shit but I did some formal training. I always found grappling when stoned made me gas a bit easier, if I am not overly stoned I probably had a better game from bottom guard but anything else was worse, not heaps worse but definately affected.
Drinking definately affects performance and coordination, seems to increase stamina for me in grappling but decrease striking stamina.
Once I had a boxing fight with a mate after smoking some meth and I felt like I gassed quick because I was overzealous at the beginning and didn't pace myself well. I was quite unfit at the time (although less unfit than I am now

) and it took a long time for my heart rate to slow down after the fight. It was a bit uncomfortable at one stage.
I also had an experience about 2 years ago when I snorted a shitload of ritalin for the first time since high school and had a grappling match with a friend who I often practised techniques with and fought. I was amp'd as and was very aggressive, beat him rather easily where normally he would have a slight edge on me and win more often than me. Afterwards my heart was pounding and I felt so dizzy. I went and was dry heaving in the toilet for like 5 minutes and had to drink water and shit. Was very unpleasant and if I had dosed much more rits it could of been ugly. The negative after effects were probably only so bad because I hadn't used the stuff in so long and took a pretty high dose because I used to use shitloads. I still feel because of my experience boxing on meth and a couple fights I regrettably got in that stimulants give you more energy at first but they don't improve stamina as much, and they definately make for some post exercise discomfort.
When I was 14/15 I used to dig smoking weed before I pumped iron at first, but eventually just ended up ditching gym. My results started stalling as soon as I began this habit but I didn't give a shit because gym was a godo excuse to fuck off for a few hours and be high.
Its funny I have never been a sporty person despite some martial arts and powerlifting phases, I didn't think I had much to say on this but it ended up a pretty long winded post.