Statistics have showen that people who are "regularly
exposed to cigarette smoke in social situations" have
a "significantly increased risk of lung disease", which
is assessed at about 50%. These diseases do not include
lung cancer; what they are referring to is bronchitis,
emphysema, or even "respiratory congestion".
Also, the period of exposure that they mention seems to be
extremely high. The main concern with second-hand smoke
is for people who already have, or are predisposed to
respiratory illness.
Another fact that was interesting: The annual costs of
smoking (health costs and lost productivity)
exceed $100 billion in the United States alone.
Enough.
If these figures don't scream it at you, here's a brief explanation. More than any of the other inflated estimates and twisted factoids, the second-hand smoke argument is really without base. This information also does not consider the other "poor living choices" that the people who spend 5h every day sitting in someone else's smoke clouds are making; people who have asthma should know better too. (This is addressed at Why I hate smokers.)
Some research on the impact on the respiratory system of smog and city pollution showed the increased risk of lung disease to be comparable to and even greater than that of "second hand smoke". The idea looks even more ridiculous when you see that all of the "increased risks" for the other warnings are based on a lifetime of heavy smoking. (For the real reason behind all this propaganda, see the last fact in the <pre> above.
If you drive a car, you are polluting my air.
If you use electricity, you are likely making use of a plant that burns fossil fuels, and polluting my air.
If you buy mass produced goods, you are making use of factories that are polluting my air.
This list could go on and on.
I'm no evironmentalist, but until you've fixed those behaviours that are fucking up my air quality, don't come bitching about the µgrams of my exhaled smoke you're breathing in. | 
