Response from the site administrator
jamonjoo, 19.07.2012
According to the Google Maps API Terms of Service you are required display a Google map when using the Google Maps API (including driving distance calculations). see: http://code.google.com/apis/maps/terms.html
... But even if possible, having to do that for every one of the possible 1,000,000's of listings for EVERY search would kill the server and make it expensive to run. ;)
This might be possible in the future if I can find a 3rd party service to calculate distance for all user as a listing is being saved, then cache the results, but then each new user needs to have it calculated also, so back to square one.
[Edit:] After some thought, usually directions are a series of right angles, so calculating one big right angle should get a good approximation.