Fake fog makes me cough - I love it, but I can't be in it for too long, and I know I can't be the only one otherwise places like Knott's Scary Farm wouldn't have all those warning signs outside their mazes (which fortunately for me never have a lot!). As long as its low to the ground and not too thick, it would be an awesome idea. Too much, though, and I might not be able to get through a long line without having a (small) coughing fit. I had trouble breathing in one haunted house that was FILLED with it, and when I saw Avenue Q, two songs after a song with fog effects that poured into our row (2nd row) I was coughing through the first act closer. For some reason, it just doesn't mix well with me.
Just remember those of us who can't handle fake fog! Water-based mist - that's good!