Google Earth is pretty freaking cool. There's other places to get satellite imagery but Google Earth wraps it into a package that has pretty much endless possibilities. I downloaded it last weekend just to see what all the fuss was about, and realized that I could use it to measure distances. A bunch of us from work swim one night a week in Lake Washington and we've always had to guess the distances between two docks that we do laps between at about 50y. I fired up Google Earth, found some football fields to make sure that it was accurate to short distances (it is!) and found our little swim spot.
Sure enough, it's 50 yards alright.
Other people are using it for cool things too. For example, they're creating detailed maps of each of the Tour de France stages, like Stage 15. Given I'm headed over there, I might map our journey as well. So cool.
It's great when something comes along that really sparks your imagination. Need to measure your property boundries, or your favorite run course, or the change in altitude? No problem. Wanna take a closer look at Area 51? No problem.