Google’s documentation for the new Google Earth plugin and API are now live.
https://code.google.com/apis/earth/
https://code.google.com/apis/earth/documentation/
https://code.google.com/apis/earth/documentation/examples.html
Here’s Google’s video of the new plugin:
Also, Brady Forrest at O’Reilley Radar has a good overview of the new announcement. [UPDATE June 6th: See more thoughts on the API.]