Earlier, I wouldn't know how well I was running, because I had no idea of the distance I was running or the speed. I run on urban roads and there are no measurements as such.
Google Earth has proved to be a wonderful tool in informing the exact distance (in meters) I was covering.
Here is a snapshot of one of the roads I run on. Its military area, part of which is accessible to the public. Junta from my locality go around for walks and many kids play cricket on the roads. I had no clue how long it was, until I had a look through Google Earth.
I was also able to look at the actual marathon route, and figure out how fast I should be running to get to certain milestones along the way.