gCensus: Google Earth + US Census GIS

http://gecensus.stanford.edu/gcensus/index.html

from that site:

<quote>

gCensus is an effort to make geographic data freely and easily  
accessible to the public, without the need for expensive GIS software  
packages. With Google's excellent free mapping program Google Earth,  
you can use this site to visualize a wide variety of data best  
displayed on a map. Currently, only the US Census 2000's Summary File  
1 (displaying population characteristics such as race and age) is  
available for mapping. I hope to have additional data sets, such as  
income (Summary File 2) and voting statistics, available soon.

# Is gCensus Free Software?

     * Yes! I haven't gotten around to doing any proper packaging on  
it (it's a pretty involved application, written in a variety of  
languages including Perl, PHP, PL/PgSQL, and JavaScript), but my  
intention is to release it under an OSDL-compliant Free Software  
license when I can get the time.

</quote>

A nice article on the project development is at ExtremeTech.com:
   http://www.extremetech.com/article2/0,1697,2102559,00.asp

And yes it was on /. so most of you have probably already seen this:
   http://developers.slashdot.org/developers/07/03/12/1337217.shtml