For anyone interested, you can look at the actual route I usually run on a Saturday by clicking here , which tots up to an Olympian 18.69km (11.61 miles)
Wouldn't it be handy if the distances calculated actually considered elevation too? Maybe google earth does that?
Update: Have just noticed that you can actually view the change in elevation for a given route, elevation is set to "off" by default.
Also, have just been reading the FAQ for the website and found a section on elevation in the calculation of distances:
"The google maps API does not expose data about elevation, which means that elevation changes are not taken into account in calculating the distances. Some users have pointed out that there are services available on the web which can return elevation given a certain latitude and longitude point. I experimented a bit with adding functionality to the site to show that, but wasn't thrilled with the fact that the data is only available for the US, and seems to be intermittent in its reliability. Maybe some day it'll be added, if enough folks indicate that want it, and they're comfortable with the fact that it may not be all that reliable."