There are 1001 reasons why you shouldn't smoke! Here are just a few:
SMOKING:
http://kidshealth.org/kid/watch/house/smoking.html
(This one says that smokers will have difficulty kepping up with friends who play sports.)
http://www.ash.org/
(A comprehensive site on action against smoking and reasons not to smoke.)
http://www.qsrn.com/quit-smoking/
(This one could help people who already somke to QUIT!)
http://www.healthmba.com/stop-smoking.html
(Another good site - includes advice on how to give up)