I paid attention to the fuel economy computer in my 2001 Chevy Astro for the first time in 5 years the other day. The idling thing really hit me when you see a nice "0 mpg" in the display. I saw 99 mpg displayed when braking at lights (the injectors must turn off). Off throttle coasting would show in the 50s mpg. At 60 mph with the cruise and A/C on it would show 23 mpg, turn off the A/C and it would go up to 28 mpg! With the A/C off and rolling down windows made no difference in the Astro killing the myth that windows up and the A/C on is more economical (it depends on the vehicle). I learned my avergage speed over 106,000 miles was only 25 mph and mpg was 18.1 (all that idling killed the speed and mpg averages).
It also convinced me I need to save up for a SuperMid for my Festiva!!
"If the engine ain't running it ain't using gas!"