Have you tried the route planner.? I kept seeing it, but just tried it. WOW. You just click, click, click and it measures your run for you. I'm actually on a business trip out of town in Chicago and wanted to run in Lincoln Park, but I didn't know how far my run would be.
I'm obsessing about my mileage 'cause I'm training hard for Jersey, so I checked it out. Pretty cool! Beats getting in the car...or guessing.