I do smoke, though not heavily. I never smoke on a boat or on the beach, though, and never in front of students, because I do recognise it's not a healthy habit for divers to have. (hypocrite, i know... ^_-) I avoid smoking at least three hours prior to any dive. I'll second some surprise at the numbers of instructors who smoke - at least half that I know do, probably more. (and that's not mentioning those instructors who smoke... er... things other than cigarettes, sometimes immediately prior to getting in the water...)
I have yet to meet a tech diver who smokes, though... they seem to understand better than some of the rest of us that our lungs are, indeed, a vital piece of scuba equipment, and deserve care and maintainance just as surely as our regs do...
I agree with Cancun Mark, though - something must be done about The Speedo Menace! The effects of secondhand Speedo-viewing are definitely hazardous...