Geodemographic tools allow marketers to understand the audience within the "place" where they are planning to introduce new products, services, messages and behaviors. Most of these tools have been expensive and relatively inaccessible to people working at the local level on health and social issues. The barriers for access to this information have been lowered as noted by Jamais Cascio at Worldchanging.
The system combines Google Maps with US Census data. At a very friendly interface you can enter an address, city, state and/or zip code and retrieve Census 2000 demographic (age, household income, gender, race/ethnicity) and housing data for 1, 3 and 5 miles around your target. There are no analytic tools to drill down through the data, and I don't know if you can import any other data to it as is common in commercial systems. A nice descriptive tool to add to your toolbox and an easy way to introduce geodemographic marketing concepts and systems to a broader audience. [Caution: May cause apoplexy among epidemiologists who will demand 'proof' of its reliability and validity.]