Some very interesting info can be gleaned from this Google Map Hack.  Hat Tip to Evangelical Outpost for this dandy of a link.  As EO says:

#468 Google Map Hack —  The Google Maps/Census mashup
from AnalyGIS and SRC adds census information from the 2000 census to
the Google Maps interface. Just put in your address and you can see the
population, income, and housing statistics for your area in a 1, 3, and
5 mile radius of your home.

Enjoy.