Recent Google Earth/Maps updates have a few API-related bits I wanted to highlight here — Maps now groks web-based KML files (example), and its API can do Geocoding (which is fully explained on the Maps API blog). For tinkerers, check out this earthcode.com blog post detailing some Rails/Maps/Geocoding integration:
"Why the lookup web service? The Google Maps API doesn't just let you map an address. You need to supply the Maps API with a longitude and latitude to place a marker on a map (or even to center a map on a city). The geocoding web service translates a valid address into longitude and latitude; you can pass the result to the Maps API."
Also, the Maps API now supports fancy zooming.