There are many interesting ways to use Google Earth: one of them is to overlay data and to explore the world through data collections. As Google puts it, Google Earth is "a powerful tool for viewing, creating and sharing interactive and highly visual location-specific information".
There are many useful layers showcased in Google Earth's sidebar, but you can always discover more in the new Google Earth Gallery. You can find information about word population density, explore the state of coral reefs around the world, see a simulation of Hurricane Katrina, find how the temperature changes over the time or visualize the world's oil consumption.
There's also a Google gadget that lists new layers every day.
2 hours ago