The fairly recent "terrain" feature in Google Maps now plots contours as well as hill shading. The only problem that I can see is that the contours are in feet in the UK whereas feet are only really used in the States. Even in the UK where we still use miles for our roads, looking at familiar hill heights in feet is very off putting. When I looked at other countries (Kenya) the heights there were in meters.
"Contour lines are lines drawn on a map connecting points of equal elevation. If you walk along a contour line you neither gain or lose elevation." The other method used for representing terrain, "hill shading is a computer based mapping technique that shades each area of the surface to proportional to the amount of light that would be reflected off the surface from a light source at a specified location, usually to the northwest of the area of interest. Hill shading produces a planimetrically correct map that looks like a three-dimensional view of the surface."
Back in April, Google's geo blog mentioned some practical uses for these features. "Now, at a glance you can see the height of the world's peaks, or plan your next camping trip. Contour lines can even help you find a flatter bike route for your daily commute, which is key if you live in a city like Seattle."