Actually Derrick, I did some research in regards to cigarettes vs. marijuana as well. You see, despite cigarette companies having you believe that it is solely tar that causes lung cancer, the real danger is radioactivity - in fact, I recall seeing on television that radioactivity, not tar, accounts for 90% of all smoking related lung cancer, at least 90% that is. Tobacco is fertilized with phosphates rich in radium 226; this is added in addition to the fact that many soils have a natural radium 226 content. Radium 226 is decomposed into two 'daughter' elements, lead 210 and polonium 210. These now airbourne particles attach to the leafs of tobacco plants. Polonium 210 and lead 210 deposits accumulate in the those exposed to cigarettes. Polonium 210 is the only component of cigarette smoke which has caused tumors when inhaled by itself.
All this radioactivity is not present when smoking this plant. In addition, MJ has 33% as much tar. Also, MJ is an expectorant, meaning it facilitates the secretion of mucus and other matter from the respiratory tract. I am not saying that it WONT cause cancer, but it definitely is not capable of being compared to the damage caused by cigarettes. Not to mention, in most cases I would imagine one smokes many more cigarettes then they would marijuana.