"Unype Facebook application lets Facebook users roam around inside Google Earth and see/interact with each other." More in Unype's blog post. It's not yet quite as exciting as it sounds, mainly because of the Google Earth's limitations -- no real-time movement or animations, for example, and not too many Facebook users either, but a very exciting step nonetheless.
Unype has also developed chat bots that can live inside Google Earth: "You can park your bot and leave your salespost ( hotel, house for sale, car dealership, resort, or simply a store ) and go away. The Unype bot will talk to your visitors for you and keep a log of what happened. The brain is completely programmable by a simple text editor and a little knowledge of AIML so you can customize it to say exactly what you would like it to say."
Now suddenly all those millions wasted on marketing experiments in Second Life don't look so quite wasted.
And here's a long article in a recent issue of Tech Review about how the merge between Google Earth and Second Life-like world is inevitable (free reg).
Rumor: Google Planning Virtual World
Google Earth Becoming Virtual World, with a quote from Jerry Paffendorf: "I would expect to see someone using Google Earth as a virtual social space by the end of the year."
Google Earth Compatible With Other 3D Environments
Whirlpool Offers 3D Models of Appliances for Google Earth