Groovy Mother points to a cool Google Maps / Census data (200) remix created by AnalyGIS and SRC using a 'Demographic API'. I'm not sure if MSN's Vistual Earth has something planned along these lines , but it would be nice... :-)

This is the data set for the 15 mile radius around my home in Redmond, WA.  Very different to what my London home data (not covered) would look like...

 Total Population15,28065,432181,189
 Total Households6,41826,99074,215
 Median Income$65,826$66,985$66,079
 Average Income$75,795$87,375$89,208
 Median Age33.1034.0035.40
 Male Population7,53532,95590,637
 Female Population7,74632,47790,552
 White Population12,38652,383147,514
 Black Population2649842,773
 Am. Indian Population79335848
 Pac. Islander Population24129356
 Asian Population1,6117,87319,846
 Other Population3881,6064,113
 2+ Race Population5272,1215,740
 Hispanic Population1,0103,7509,464