We once got stuck in a smoking room after requesting non-smoking, so it does happen. They weren't going to move us (said their was no availibility) but I persisted. I said it didn't matter what resort, as long as it had a bed and was non-smoking. This was July 4, 2004 at Pop Century. It was just for one night before we checked into the Poly. After much back and forth, they finally "found" us a non smoking room at Pop.
I know make sure to say I need a non-smoking room for medical reasons. We do not have asthma or breathing issues, but we just can't tolerate the smell. I think it is ridiculous in this day and age, with all the health implications of second hand smoke, that Disney cannot guarantee non-smoking rooms.