You've probably heard about FlashEarth, the site that lets you compare the satellite imagery offered by Google Maps, Yahoo Maps, Microsoft Virtual Earth, Ask.com and more. Now you can use FlashEarth directly from Google Earth thanks to a layer created by Barry Hunter. "As you move around the globe a little white arrow follows you around, simple click it to get an approximation of the current view in FlashEarth in a popup balloon."
This could be useful if Google Earth doesn't have a very good coverage of a certain area or you just want to see the same image from a different perspective.