While Google Earth is still around, it makes sense to maximise its usefulness. The Google Earth Blog shares some nice pointers how to tune your GEarth installation in case you experience performance issues.
They’ve also recently covered a company called KMZmaps.com which offers a set of custom KMZ overlays for use in GEarth. Honestly, I think most of them are *#%& and not worth even the small amount that they charge (though, the nightlights overlays look kinda cool). Instead, I strongly recommend the Blue Marble overlay, which is free and described here. It gives you a nice globe with a satellite picture mosaic (from satellites Terra and Aqua), much prettier and cleaner than the usual GEarth patchwork (when you zoom in you still get to see the high-res imagery offered through Google). I used the Blue Marble overlay to whip up the graphic in this post.