A colleague friend of mine once called Google Earth 'the ultimate non-game'. I've played with it some time ago, and I have to say that I agree. In fact, I included it as part of the literature review for my MA final project (which I might publish here), and I paste below a passage about it.
Recently released Google Earth is a real-life application that also can be used as an interactive toy or non-game. An interactive terrestrial globe, it allows the user to navigate around the world and zoom in to see, in real-time, detailed territories made from high-resolution satellite photographs rendered into a bump mapped 3D terrain
What seem to attract users to Google Earth is not any practical aspects of it, but the mere pleasure of navigating around the globe and seeing both familiar and unknown places in a very realistic way. This very pleasure, detached from any functional needs, is what makes blurry the line between the application it is and the game or toy it is used as.
Another interesting thing is how it is probably not perceived as a toy by its users - something the game industry could aim for, in order to attract different audiences.
In case you haven't tried yet, the link for the application is http://earth.google.com/.