Oh, no doubt the radiation is likely a non-issue, but there is more merit to the fear in that than from Wifi and cell phones. Like you said, if you're a frequent flyer it could add up though. I definitely take issue with them not being forthcoming about how much radiation each scan is exposing you to though. Likewise, who knows if they retain the images they obtain or anything like that.
Another issue is that in the cases where people refuse the body scanners, the TSA personnel have allegedly responded in a pretty hostile manner.
They're not very open about things, and they don't take kindly to people asking about it either, and so I think the scanners just underline the general feeling of hostility that people get from the TSA.
I've gone through the body scan, and I'm iffy. Its not that much of a hassle, but its not a pleasant experience. Personally, the hassle of flying (the TSA is just another point on the list) isn't worth it, so I'll be abstaining from it unless its really necessary.