Seattle

IT is one of the oldest tricks in an Internet company's playbook. Concoct a tool that gives the public new statistics on something - the quality of a restaurant or a toaster, say. Then watch visitors flock to the data and worry about accuracy later.

Few such tools have been as controversial as ones that show people the market value of homes, using software algorithms to do the estimates. Homes are typically people's most valuable asset, so emotions run hot when these estimates are seen as too high or too low.