Ideas
Art
  1. •Example KMZ file
What could be more fun than decorating the world? With overlays you can do some amazing things(especially with varying degrees of opacity )  It will also map the images to underlying 3D geography which makes things really neat.
 
You’ve also got the option of using Google SketchUp to create 3D models and be able to put them directly in Google Earth.  The models themselves are a good way to look at perspective and the detail in many of them is pretty impressive.
Math
  1. •Example KMZ file
 
There’s a lot you can do with the measurement tool.  You’ve got conversions, addition, finding the area of shapes etc.  
 
Using placemarks would be a fun way to spice up word problems.  I’d put the question in the placemark’s info window.  If a train is leaving Albany at 50 mph it’s bound to help some of your visual learners to really see the icon of a train in Albany.
 
Math scavenger hunts would also be fun.  Have problems in placemark info windows and name the icons with the answers to different problems.  Students would then have to answer the answer the questions and proceed from place to place based on their answer.  You could have them log the locations they visit in order, measure the total distance or even have them end up spelling a message using the measure tool.
English
  1. •Example KMZ bio files for Bob Marley and Hank Williams.
I think the potential for English is also quite strong.  You have basic ideas like showing book settings but there’s also the potential to use the program to construct 3D information rich replicas that follow the story.  
Imagine plotting out the locations from Around the World in 80 Days and having the kids add information about each area as you get to that portion of the novel.  
I also like the idea of using custom icons and overlays to create a story that reluctant readers/writers would be interested in.  
Using this program as part of a biography has been done well already using people like Bob Marley and Hank Williams.