Ionization is not the only mechanism known to cause cancer. I don't claim that microwave exposure causes cancer by some other mechanism. I just think it's one thing to say "Microwaves are not ionizing radiation." and something different to say "Microwaves don't cause cancer." That said, I'm fairly comfortable with my microwave exposure, which is likely higher than average. My exposure to x-ray and beta radiation is also a bit higher than average, but I don't worry about that either. I find it annoying that there is a group of geeks with a hair trigger response to any talk about microwaves ready to inform everyone that microwaves can't cause cancer because they are not ionizing radiation. Well, neither is asbestos, and they only figured out in the last 10 years or so why asbestos causes cancer. Yes, they've known for a long time that it seemed to have something to do with the irritant effect of the fibers over time, but the mechanism was not clear. Most irritating things don't cause cancer. But recently the biological mechanism between irritation and cancer was found for asbestos. At any rate, I base my comfort level with my microwave exposure based on the fact that studies relating microwave exposure with rates of cancer seem weak.