I got the free download and played around with this, and it is really cool. You definitely need a broadband connection to make it worthwhile, and even then you need some patience as large images are downloaded.
World Wind lets you zoom from satellite altitude into any place on Earth. Leveraging Landsat satellite imagery and Shuttle Radar Topography Mission data, World Wind lets you experience Earth terrain in visually rich 3D, just as if you were really there.
Virtually visit any place in the world. Look across the Andes, into the Grand Canyon, over the Alps, or along the African Sahara.