I love it when the engines take fun products that they build and integrate them together to make the other products more powerful. Last night Google's AdWords blog wrote a blog entry named Use Google Maps to target your customers. That is exactly what it helps you do.
How does it work? After selecting customized targeting when editing or creating a new campaign, you can now define your location with just a few clicks of the mouse. First, click-and-drag the map and zoom in to find your location or desired target area. Then submit a distance (we recommend at least 20 miles) around your location target. A circle will appear on the map to confirm the region – so you can be sure your ads appear to potential customers in the exact neighborhoods you want to reach.
More detailed information on How does customised targeting work? (hmm, this available in the US market ;) ).
Only forum discussion I was able to find at this time, was at Search Engine Watch Forums. I wonder if the AdWords users, both pros and newbies, will find this useful or not.