I read the same thing about building your immunity by eating it, but that's too scary for me!
Luckily, we have lots of jewelweed growing on our property, and rubbing that on your skin prevents the rash. If I'm in a spot where there there isn't jewelweed, I bring a milk jug filled with water, a bar of soap and a small towel. It's good to know what kind of soap to use, though, thanks for the tip!