A park in my hometown was labelled as actually being in a larger nearby town. In fact, Gogole Maps didn't seem to think my hometown existed (it's not really a small town, either). This wouldn't be a problem, except that after you've searched and found the location you wanted, the discrepancy would cause the permanent link to fail for some reason, making it effectively impossible to send the directions or location to someone else.
So, I filed a ticket explaining the whole situation and forgot about it.
This was in October of 2009. In February of 2010 (long after I forgot about it), I actually heard back with this message:
Your Google Maps problem report has been reviewed, and you were right! We'll update the map soon and email you when you can see the change.
Then, in April 2010:
Google Maps has been updated to correct the problem you reported. You can see the update here, and if you still see a problem, please tell us more about the issue
So, it took quite a while, but they DID actually look into it and fix it.
I just thought that was interesting, given the usual "Google has no humans in customer service" tales.