OK, here's today's climb up Slug Gulch Road in El Dorado County, CA. I measured lots of grades in the teens. As usual the Garmin went nuts and showed grades that don't even exist on paved roads, so I'm going to guess that the actual max grade on this climb was 16% or 17%.

This video has GPS data overlay so you can see the speed (inaccurate at times due to foliage interfering with satellite signals), heart rate, distance, altitude, and percent grade.

http://www.youtube.com/watch?v=I_Q8R-t_6D0