What’s interesting about gCensus is the fact that the project itself is an interface between Google Earth and Census data. It was created after a student felt that it was ridiculous for have to have professional GIS mapping software to plot census data. So he created a proof-of-concept mashup between Google Earth since it can do 3D polygons, and the data provided by the Census. Take a looksie.
Extremetech < gCensus