Mentat23: Which JWH are you referring to? Or is that an opinion on all the JWH's?
It sounds like the JWH's themselves inhibit cancer growth, but we shouldn't consider that an guarantee of safety. It's been brought up in ADD that they might be metabolized into some much less friendly (carcinogenic) things, but that risk is certainly not proven.
Until more data on long-term safety comes in, I don't think we should assume it's entirely safe. However, for most of us the alternative is smoking plant material, which is not healthy long term either. JWH's don't even need to be vaporized, can just eat them...
CP-47,497 and CP-55,940 look less likely to have concerns with the metabolites, but they're much harder to get (which seems odd, since they look easier to make than JWH-###, and are just as potent by weight, yet everyone and their mom is selling JWH-018, while the CP's remain elusive). I have an order in for a gram of CP-55,940, but i think they just took my money.