Having worked in HR for 32 years, I am pretty well versed in what kinds of things can be asked on applications and what can and cannot be asked in interviews.
Any questions asked during interviews which do not pertain to an individual's qualifications for the specific job can be misinterpreted by the interviewee as being discriminatory.
If you want to ask me whether or not I am a smoker during the interview process, you damn well better be prepared to be able to document the fact that I can not perform the required duties of such job merely because I am a smoker.
The second you ask me any question relevant to the legal practice of tobacco use, you have now opened the door for me to file a legitimate claim of discrimination with the EEOC.........
And I now fully understand your tag line ;-)