My other reason for wanting to use Google Earth is that it fills a lot of functions in one program that other map only, or navigation only programs don't do.
This sounds cheesy, but since it has the power of google behind it you can do location based internet searches.
For example me and the wife love to eat a Cracker Barrel when we travel. I had no choice on my way home from my trip but to make a overnight stop in El Paso, TX. There were three Motel 6's in town (pet friendly).
Logic told me I should stay at the one on the far side of town to beat morning traffic. But looking at the location on google earth, it was between what looked like a junk yard and a rail station.
Then I noticed that one was right next door to a Cracker barrel because it popped up automatically on GE. I was able to survey the area and find it was all new shopping and was a nice area of town. It made the stay much more enjoyable. (Morning traffic sucked of course though)
BTW here is a link to the google maps overlay