Still, they're going to have to grope me: I am not going to go through one of those damn machines
I feel much the same way. I suspect that the machines are safe, but I am not confident they have been thoroughly tested so there is a risk. I certainly don't trust the TSA to tell me the truth about the true risks of the scanner.
The main reason I opt out of the scanner, though, is this. I consider both the pat-down and the scanner a violation of my rights. The TSA wants me to use the scanner because that is more efficient for them. Therefore, I will force the TSA to violate my rights in the most inefficient way possible. Unfortunately, there are very few people doing this so it isn't gumming up there system too bad right now. After going through a few pat-downs, I know the procedure well enough that I can be snarky and tell the TSA when he screws up.
Like you, I fly less than I used to because of the stupid security screenings. I'm not convinced that boycotts will influence TSA behavior, though. There are enough people that need to fly that the airlines will not simply go out of business, and they will adjust to reduced passenger load by running fewer flights. In other words, an equilibrium will be reached where they won't realize how much business they are losing because it is hard to measure how many people would have bought tickets if the security procedures were not so retarded.