The biggest problem I have with them is the "It's harmless" argument, It's been proven that they are indeed harmful. Estimated to be half as bad as cigarettes, but still harmful. I've tried one before, and it was just like breathing to me, so I tried one with a "hit" and it made be cough for 20 minutes and hyperventilate.
Both of them kill you, I prefer the real thing.
P.S the harm from them was related to particles within the vapor, Don't go asking for a source, because I read that about 6 months ago - also, if your inhaling the stuff you should of researched it yourself anyway by now. They don't have nasty chemicals, but they still give you cancer.