So I was playing with Google Earth the other day and spotted a new menu item..
View > Sun
Turn this on and you have a sun that casts shadows on the terrain! Also if you tick 'Weather - Clouds' in the layers list you get realtime clouds in the sky. I have to say it looks pretty darn cool.
You can change the time of day, and when night falls the stars come out, pretty funky eh. Increase the terrain quality in the options for smoother landscape features.
Sooo... We have the built in flight sim already, I'm now just waiting for the day when you can pick a spot and stroll around on the surface, maybe other people would be visible too, also strolling around. Develop this a bit further and you have a pretty good 'virtual world' that is modelled on the real world in real time - weather, sun and stars at least. It could turn into a more realistic looking Second Life in a few years if they take it that direction.