Thanks to the Zillow boundaries we could add a new neighbourhood reverse geocoding service to our API. This neighbourhood web service returns the neighbourhood name, city name, county name and state name for a given latitude/longitude.
Zillow have aggregated the boundary data from online resources, chambers of commerce, tourism and convention boards as well as real estate agents.
Unfortunately they have not chosen the freest creative commons license, the cc-by license, like GeoNames, but have opted instead for the more restrictive cc-by-sa license. The share alike restriction will prevent people from improving upon it. GeoNames for instance cannot use it for their own database. While it is fantastic move by Zillow to release the boundaries, the sa restriction means the community will still need another dataset with a really free license. It is a pity since it will mean a duplication of efforts and reinventing the wheel. At the other hand I am confident that Zillow will change the license as the restriction does not stop their competitors from using it, it just hampers further development and Zillow would gain more without this restriction.