I was working as a Travel Agent when Northwest started their smoking ban.
Another agent that had worked in the field for several years, said that the filter system in the planes were overloaded and filthy from smokers.
Get this: once all airlines banned smoking, the people in charge of cleaning the filters let them go, thinking that since there is no more smoking on the airline, the filters will remain cleaner longer.
Guess what: now when they go to change the filters, they are BEYOND FILTH. And that is the air the passengers breath.
BUT OMG! DON'T LET THEM SMOKE!
I know what you mean. On submarines the air handling devices drip with yellow/brown goo from the smokers. I remember as a teenager cleaning my car windshield on the inside and the towel turning brown as I wiped.