One thing I have noticed is that the api is a little different than the google maps page. For example when creating a map using a location posted to the api it must be an exact match for them to make a map, whereas in the google maps page whatever you enter for location is basically a search and it brings back a list of possible exact locations. I imagine its a similar issue with driving directions. It would be nice if they returned something that says no matching location found or if they returned the first search result even if it isn't an exact match of the entered location.
Best,
Joe