Why even follow the zillow estimates? You can do a much better job yourself in estimating market value just by paying attention to the MLS. In my experience, Zillow is less accurate that cyberhome or eappraisal.
If automated programs were to work well, seems like they would work best in a stable market. This market is anything but stable. There are two markets really: the all cash market and the FHA market which the flippers are selling to.