What is the life expectancy of smokers vs. non-smokers?
It's hard to give a firm answer to that question, in part because it's hard to make a firm distinction between the two categories. Smokers and non-smokers aren't locked into one role for life. Where do we place somebody who smoked a pack a day for ten years, and then quit? Or somebody who smokes one cigarette a month? Possibly we can compare lifelong non-smokers with people who have smoked daily throughout their adulthood, but it's easier to compute the amount of expected life lost by people due to smoking in a given year.
According to the Center for Disease Control, in an average year from 2000 to 2004, an estimated 443,000 Americans died prematurely due to smoking. (This includes secondhand smoke, and infant deaths related to smoking during pregnancy.) In fact, 1 in 5 U.S. deaths is smoking-related. On average, adults who smoke cigarettes die 14 years earlier than nonsmokers. This doesn't quite answer your question, as it includes some non-smokers and excludes smokers who don't die prematurely, but it definitely drives home the point that smoking is very bad for your health.
Fortunately, smoking is on the decline in the U.S. In 2007, 20.8% percent of the adult population smoked, down from 42.4% in 1965.