I've noticed that a lot of casual riders coast frequently-- anywhere from 10-40% of the time on flat ground. You can't do that when climbing. You have to be conditioned to pedal something very near 100% of the time, which is something best learned when climbing or by pacing riders faster than you are.
I was doing half-mile 8% climbs around 7mph. It was manageable for me, and I'm nowhere near awesome. My wife was right behind me.
