Lol Hadley, yes, I've seen some really big blunts (I saw one the size of a cigar once, but on youtube there's a video of a really big one). I'm not really being close minded, I'm just showing "scientific proof" that all smoke can wear out the cilia, which starts a chain reaction what wore out the cilia continued to happen. As the guy 'suspects' about breathing in a city with poor air quality, that is also true. Who decides what a day's dose is, anyway? That article Andrew Nelson linked to provided a clear bias toward cigarettes in that study (Really, to have a cigarette smoking history you have to smoke 6x as many cigarettes as joints, then to measure how much you smoke it's 1pack of cigarettes to every joint? Really?). You're second is interesting though, because it is directly opposite of what the article said that Andrew Nelson linked to (it directly stated marijuana use in younger age does lead to lung issues).
All I'm saying is, it's scientifically clear that all smoke wears out your alveoli. This is true for a lot of substances though. The dosage does vary from substance to substance, but the point is enough of any form of smoke is enough to give you lung issues. One (or both) of the articles I linked to stated that coughing is one of the ways the lungs try to get rid of this stuff. How many of you coughed when you first started smoking (pot or cigarettes)? That's a sign of your cilia trying to get rid of it. I still see a lot of people take too big of a hit off a joint/bong and they still cough (and they're seasons smokers!) If the argument "but I don't cough anymore" comes up, you can build a tolerance to things, that doesn't mean your cilia aren't getting worn out just because you are used to that "feeling".
Andrew: At what point did I say that it would occur from "normal smoking?" I already stated that it's eventually it will happen. Also, what point is that, exactly? One joint per week? Per day? Per hour? Your article says they measure cigarettes by the pack, yet marijuana by the joint.
Even putting all this aside, and attempting to get back to marijuana specifics: All this can be avoided if you just eat it. Hadley, I'm sure you've got stories about how much better/worse (high wise) to eat it rather than smoke it.