I'm a non-smoker, and I've never tried it. The way I see it, it's easier not to start than it is to give up. Nicotine is proven to be as addictive (or more so) than heroin - no way am I trying that! The health issue is an important one too, and the simple fact is that smoking is very unhealthy. Argue for it as an anti-obesity drug if you like, but there are other ways to keep your weight down. Jogging, or eating sensibly, for example, neither of which cause cancer or lung disease.
Passive smoking isn't proven to be particularly harmful. It does increase rates of lung disease in non-smokers, but from a near-zero level to a level just barely above that. At the same time, it's horrible to those who have to endure the smell and the irritation. It took me years to be able to cope with a smoker at the other side of a chess-board, or the atmosphere in a pub.
Fortunately, it's becomming illegal to smoke in a place of work (including pubs and resteraunts) in Ireland next month, and I welcome that with open arms. Banning smoking totally won't work, but making it totally unacceptable in company will.