AnotherEarth.org — Two globes in one

John sent me an email last week telling me about a new project he’s working on, and it’s quite cool — he calles it anotherearth. He explains it as follows:

This application gives you a number of tools with which you can easily and comprehensively compare two views of the Earth, using the Google Earth browser plugin. These include the ability to synchronize the movement of two Earths, select layers such as buildings, roads and borders for the Earths, jump to locations of your choice, undo/redo any movements, and save coordinates as a URL.

The controls are very fluid, and there are a lot of excellent potential uses for it. You can try it for yourself at anotherearth.org. What are some neat things you can do with it?
John has plans to add more features in the future, making the tool even more useful. If it were up to you, what kind of features would you add to it?