This isn't actually available yet, but I couldn't help showing a preview: the Open WorldCat Find-in-a-Library page hooked up with Google maps. For this example I did a search in Yahoo for 'McCarthy's Bar', went to the Open WorldCat page, and then clicked on a bookmarklet that shifted into the map view from the standard view. Wish I could claim responsibility, but this came from Mike Teets (head of our Product Architecture and Development groups). It should be available soon here. This sort of thing is possible to do quickly because of the open way that the Google maps is implemented as web services.
Although the gmaps bookmarklet isn't available yet, the Product works site has some useful browser extensions for Open WorldCat that have been released.