The event started in 1971 when Arthur Mullaney asked people to give up smoking for a day. He asked that they use the money they would have spent on cigarettes to give a donation to a local high school. The idea spread and the American Cancer Society made it a nationwide event in 1977.
Knowledge is an important part of giving up tobacco products. Just knowing that manufacturers add toxic ingredients to cigarettes to make them tastier can cause some people to quit. That list of ingredients includes ammonia, arsenic, benzene, butane, carbon monoxide, cadmium, cyanide, DDT, Ethyl Furoate, lead, formaldehyde, methoprene, maltitol, napthalene, and about 500 more. These products are rat poisons, poisonous gasses, insecticides, preservatives, and others that should not be inhaled or ingested. (http://www.care2.com/greenliving/the-shocking-ingredients-in-cigarettes.html)
Also helpful for those wanting to quit is having some means of support. Nicotine replacement products, counseling, friends, and family can all do the trick.
For more information, a quick search on the Internet will provide many web sites with lots of valuable information. Just search for "Great American Smokeout 2009."