WHBM,
Very rare to see it. When it does happen, you will find that the F/As have zero patience and will quickly open the door to find the source of the tobacco smell. They do this not to catch the smoker, but to prevent the potential result of putting a butt in the trashcan.
Many will recall this DC-9 accident that killed 23 people.
http://www.ntsb.gov/publictn/1986/AAR8602.htm