Regarding the earlier discussion of wether or not a gravity bong wastes weed:
I think the issue that everyone is getting stuck on is the size of the group smoking a gravity bong. Since g.b's are typically "special events", like for instance maybe your having a party and you wanna go all out for a group of say 5 people to smoke. Since their are 5 people smoking for instance, your gonna be loading the bowl a few times. This is probably what throws alot of people off when they think gravity bongs waste alot of weed. Since usually their are 3-5 people, at least when we do g.b.'s, your gonna use more weed. And since more than not most people will not handle a huge hit well, it seems as though alot of smoke just gets left over, etc.
Their are a lot of factors to consider when smoking. Size of the group, size of bowl, type of bowl (gravity bong). Since their are so many factors, it's not that easy to tell if your being as "efficient" smoking as you are in other situations.
My conclusion is that a gravity bong would get you just as high, if not higher using the exact same amount of weed vs. smoking it out of a pipe. HOWEVER, since alot of people can not handle a full hit, and their sometimes will be smoke lost during taking the hit, etc., in some cases it can use up more weed, only because of the fault of the people smoking it.
My 2 cents