I live on a gravel road and 90% of my riding is on gravel. Climbing on washboards is indeed a lot harder.
I have to disagree with some of the replies. The road I live on is part of the Great Divide Mountain bike route and is on the section south of Helena immediately prior to the infamous Lava Mountain portion and a part of the route regarded as one of the tougher sections of the 2700 mile ride. The washboarding gets pretty bad, especially late in the summer, due to the vehicle traffic going up to an alpine lake campground. The worst washboarding is on the steeper inclines, worst on the right side of the road, where the trucks climb and less so on the left side where vehicles descend. The washboarding gets bad enough that on my pickup truck the rear window shook loose from the camper top last year - and I was crawling along. The flat sections are not as washboarded on this road. Whoever stated that washboards do not occur on inclines is just wrong. . I have also ridden on washboarded flat sections on some other gravel roads, however.
I just try to find the best line, get in a low gear and gut it out, but riding washboards is definitely not the best biking experience.