According to the Google Geo Developers Blog:
The new Google Maps API has been released as part of Google Labs, indicating that it is not yet a mature release, although we expect that the new API will likely become the preferred API for developers, given its speed and performance improvements. Google has also provided a summary overview of what is new in V3 of the Maps API:
- Chrome and iPhone Safari mobile added to our supported browsers. Your mashups will also work on Android-based phones with the recent update, but you may notice some issues, like the "View/Save Image" dialog showing unexpectedly. We're working with the Android team to fix this and improve the end user's experience in interacting with the map. We could've waited until it's perfect, but we really wanted to get an early release in your hands and start getting feedback while we fix up a few remaining issues.
- No keys required. You can now copy 'n paste code easily or embed in RSS readers, for example, without getting key errors.
- Default UI is enabled automatically. We'll provide default UI controls and behavior (and we'll update them) so your mashup can keep up with the latest and greatest changes we make to Google Maps. Of course, if you've got customized controls you're happy with, you can disable the default UI updates.
- Namespaces. Everything is always in the google.maps.* namespace and there is no "G" prefixed variables in the global scope.
- Geocoding API has been overhauled based on the feedback we've received with the existing implementation over the past three years.
This is certainly an exciting release, given that the Google Maps API is the most popular API (1,697 mashups!) in our API directory. Google has set up new documentation and a new Group for developers to get started with the API.