Incidentally, I think Zillow is just one of what will eventually be a number of such programs, and those programs will improve as time progresses. How useful Zillow is to people will depend on how they use it. If they’re using it solely to get a Zestimate then they’re not going to be happy at all because of the inherent limitations.
The cool thing about Zillow is that it provides a portal to the data that hasn’t been as readily available before. As with most data sources the trick has always been to figure out how to use the data.