Look at the neat things Andy Hall has done with Google Earth over at his consistently interesting Dead Confederates blog. Through "image overlay," and careful scaling of the original to align with the Google image (when will someone come up with an App that scales these images for you?), one can get a reasonably accurate look at how a historic image fits into today's satellite view. Pretty damn cool. Have at look at what he did with the location of Henry Wirz's gallows (at the Old Capitol Prison -- see the full essay on the Wirz Execution photos here) in relation to today's U.S. Supreme Court building. Likewise, the overlay of 1865 Galveston with the modern view. The application of Google Earth tools to historic documents is as unlimited as our nearly infinite capacity for avoiding doing any real work (or as Andy put it, the functionality is limited only by the imagination of the user).
Thus far, with respect to Google Earth, my imagination was limited to creating three Civil War quizes in which participants view an overhead view of a part of a battlefield or significant landmark -- just out of context enough to be disorienting for some -- and try to guess the Civil War location. If you haven't given it a shot yet, links to the quizes and answers are given below. Quiz #1 centers on fairly famous battlefield features, without clues, while the subsequent two quizes include more-or-less useful clues.
Google Earth Quiz Number Two is here -- (the answers for Quiz Two are found in the last of the 3 comments attached to that post).