I love using Google Earth to teach how GPS devices work. In fact I taught some 6th graders about this very fact this time last year :) It has the "cool" factor of flying through the sky like superman to your house, and is educational to boot!
They have just added a new component to Google Earth that lets you search the sky - just like you search the world. How freakin' cool is that! I can imagine a multitude of different ways this can be used. The NYT story discusses the more that one million photographs it took to piece together the sky!