<< Recently Google Maps introduced the ability to perform searches by neighborhoods. Neighborhoods tend to be somewhat informally defined but well recognized in certain cities. Neighborhood search is now available in fifty US cities, with more to follow. >>

http://google-latlong.blogspot.com/2007/05/posted-by-david-tussey-product-manager.html

Via:
http://blog.wired.com/monkeybites/2007/05/google_maps_now.html