After riding around all day on the KHS Green, I noticed something, ahem, interesting. I've no idea how to put this delicately, so I won't even try: My bottom hurt like hell the next morning! It did not seem to be a muscle pain, but rather a pain from the imprint of the seat.
When returning the rental bike, I gingerly asked one of the Cambridge Bicycle employees about this. He replied that the sore butt is a natural side-effect of the relaxed-style sitting position: Because the seat is so much lower than the handle-bars, the body's weight gets distributed predominantly to that part of the body. The butt gets pressed into the seat, eventually becoming sore (especially after hours of riding).
This explanation makes sense. But why is this "feature" not mentioned on any of the reviews and weblogs that praise Dutch bicycles and relaxed-style riding?... I wonder whether the quality of the seat might have something to do with it as well. Either way, I thought it would be useful to provide this tidbit of information!