First, and foremost, you can now use KML files to overlay your Google Maps. Check out the developer documentation for details, but basically you can put a KML file out on your server and it will be rendered as part of the Google Maps page that you provide.
Next, the API has been extended to provide geocoding, whittling away at the feature differences between Yahoo! Maps and Google Maps. Although I haven't played with the extensions, Google representatives claimed function in the US, Canada, UK, Japan, Germany, Spain, France, and Italy.
Rounding out the announcements (not counting yesterday's coverage of Google Earth 4.0) is the announcement of the availability of commercial support for Google Maps, finally providing a route for companies to use it for commercial use. Fees, unfortunately, are pay per transaction—just like everybody else, but at least it's now available. Details at the Google Maps for Enterprise site.