I'll throw my two cents in that the USGBC should consider prohibiting smoking for LEED certification. I understand that pressure from the tobacco industry might prevent an outright ban. That industry has long pushed for controlled smoking rooms as an alternative to smoking bans. I suspect this is why smoking rooms are an option in the existing prerequisite.
For a smoking room to be effective the ventilation system must be balanced. Even with enhanced commissioning, there simply could not be enough testing to assure that a displacement ventilation system is operating as it should. Additionally, regardless of reduced PPAH & RSP levels in non-smoking areas, PPAHs and RSPs can still escape into those areas.
As a building operator, I cannot imagine consciously subjecting any of my occupants to carcinogens, even if they volunteer for it. My goal as a LEED AP is not only sustainable construction and operations, but healthy work environments, as well.
I imagine the systems required for smoking rooms also decrease building efficiency. Even if it's by a single percentage point, that flies in the face of our goal to reduce our impact and increase efficiency.
LEED is voluntary. Unless your city mandates certification, it is a building owner's choice to pursue the rigorous standards put forth by the rating system. I do not intend to alienate smokers. My only intent is to provide healthy, high performance buildings. You wanna smoke? Go outside. Just make sure it's 25' away from doors, vents, and operable windows. :)