Another cacher is in the process of creating software which can plot cache density in Google Earth. It was designed for Linux, and I have not been successful getting that to work yet, but I am getting closer. Anyway I've been playing with a script of my own to create the Google Earth file.
If you want to play with the actual Google Earth kml file here it is: mainecachedensity.kml (469K)
This particular file has all caches ever placed in Maine. The blank areas have no caches, the dark areas have a few, and the red/purple/blue have more, in that order.