I recently removed my bicycle computer, but when I used it, it gave a rolling average of about 15-17 mph on mild to moderate terrain/traffic. My real average, though, once you factor in bigger hills, traffic lights, riding in the door zone, etc., is almost always about 10 mph. It's like Hubble's Constant or the speed of light: no matter how fast or slowly I ride, over any longer distance in an urban environment, the average is 10 mph. It's not exactly a rocket ride on the MUP at 6:00 AM, but at least it makes trip planning pretty easy...