I think of Google Earth more as a platform than a tool that's useful by itself -- you can really build cool things into it, rather than the more simple layery things that you can do with GMaps. It's like a really cool bucket. We've done some building of 3D structures, for example, to represent stuff related to various geographic locations, and there are more information/data layers available, too. And I love flying through interactive routes.

But Google Maps seems to me to be more of a tool that gives you content that you need or want when you need or want it. I think I'm doing a poor job explaining my perceived differences. :-)