There are some indications that RF has ill effects on humans, at least in certain configurations or environments. Here are a few references taken from the top search results from Google Scholar. It looks like there's a lot of debate on this issue, and support for both sides.
My personal opinion is that cell phones are safe, though I don't put mine in my hip pocket or otherwise in close proximity to the soft, permeable tissue of my testicles, nor do I sleep with a phone near my head. I also hold the opinion that amplifiers and things like that should be a meter or so away from the body, even the legs, where though there are no major organs, blood constituents are produced in the bone. I also recommend using external antennas for even handhelds, if they're used more than once in awhile. There was an old article on this topic written by a ham / medical doctor, I think in the ARRL magazine, but I don't remember the name of it.
Remember that RF decreases at the inverse square of the distance of propagation. Pushing the source a little away from you makes a big difference in the amount of energy that permeates your tissue.