I was thinking about this thread on my ride yesterday! Not a washboard road, but some pretty rough mountain bike trails. A few of the single-track trails were fairly fast but heavily potted, and there was just no way to avoid them. That was the most brain-rattling ride I've had so far. I probably should have let some air out of the tires (47mm tires at 30-35psi), but I'm not sure even that would have helped much.