My favorite Non-hidden features:
Endagered species: The google earth program includes information on various types of endangered species from around the world. to enable it, Go down to "Layers", Go to "Global Awareness" and Check "ARKive: Endangered species."
Shipwrecks: See info about various shipwrecks around the world. google earth tells you where it happened, the name of the ship, and sometimes a bit more. to enable, go to "Layers", drop down "Ocean" and check "Shipwrecks"
Map of the Moon: On The Upper tool bar, you will see a picture of a planet. drop it down. click on mars or the moon.
Add-ons: to download the add-ons, google add-on, plus the name google earth. for example: Earthquake add-on google earth.
To run add-ons, in google earth click open. your add-ons will be in a google earth .kml or .kmz file. go to the folder where they are saved. click open.
Earthquakes: See where earthquakes have happened, their strength, and when they happened.
Population Density: Self explanatory.
Scroll Down for the best hidden google earth feature EVER!!!
FLIGHT SIMULATOR: fly over the Rocky Mountains! fly in the grand canyon! flying over cities is lame though, they are all flat.
To open it, press Ctrl+Alt+A. it will open up. click the help button for controls. you can take off from a run way or from your current view.
You have two different planes, an F-16 and an SR22. there is no external view, unless you download plane add-ons. google "Plane Add-ons for google earth flight simulator google earth blog"
open one up just like the other add-ons, and you will see an animation bar at the top. click the wrench, for settings. check "Loop Animation." press OK. go to the animation bar, and press play. run the flight simulator like normal.