First off, the program "Google Earth" is still in Beta version, which means it is horrible. I tried it, trust me it is not good at all. There is no updating on the program at all which leaves me to wonder exactly where they are getting their images from.
For an example, I'll take this ladies house that I worked with. Her house was built approximately four years ago and Google Earth, when I checked it like a month ago, DID NOT have it on there. It still showed the thing as an empty lot. And YES, it was the right place, I've found multiple other things on Google Earth in this area so I know what I'm doing with it.
Now on the other hand, NASA World Wind, that is a good program. It can't "zoom in" as close as Google Earth can but it is actually the real thing. And for those who asked, here is a picture of the Gap:
(Correct me if I'm wrong Gap Goers)