Prosecution would be futile. The problem of proof Passengers are arrested or detained, mostly if they refuse to obey a flight attendant or act unruly. It's hard to say how many. The FAA, though it receives reports and levies fines, does not track smoking-related arrests. They are handled by a variety of law enforcement groups.
Pilots can and do divert the plane because of a smoker on board.
For instance, one incident report submitted to the FAA said an America West flight returned to Dallas after a woman smoked in the bathroom and in her first-class seat. FBI officers interrogated and released them. Being delivered into the hands of the law doesn't necessarily mean being booked, according to FAA reports and fliers' observations. Sometimes a get-tough crew can make a difference. Smokers' tricks Passengers can go to great lengths to foil lavatory smoke detectors.