We live just south of the New Hampshire border, and about a quarter-mile from a granite quarry. Apparently granite is either a great sponge for radon, or it tends to trap it. Generally, if there is granite in the area, there will be radon. Unfortunately radon is oderless, and clear and so there is no way to know its there unless it's too late.
Either way our house has a radon extraction system installed. It's not rocket science nor super expensive. Just a sealed pipe through the basement floor with a muffen-type extraction fan mounted outside to maintain a slight vacuum under the basement floor. You can just see the manometer on the pipe with the bright red liquid in it.
Radon has really only become an issue since the advent of very tight, draft free houses. If your windows are always open, or if you have a lot of drafts in the house, it's not a big deal. But if you have a tight, energy efficient house, the radon won't get blown out.