Http://www.zillow.com/zestimate/#acc

Programming algorithms based on skewed data. The better the data it has to work with, the better the algorithm works. . :)

I like to compare redfin and zillow results to get an approximate price range for the houses i'm looking at prior to pestering a realtor for comps..

It actually works quite well in larger subdivisions with uniform housing stock, the opposite is true in rural areas or homes that are a little different than the comps or areas where the housing stock is very diverse.

because it makes people feel good when they know their house is WORTH SO MUCH!! thus, it will be used more often than other sites that show "such a low value".