Zillow is totally out of whack for my zip code. Unless, of course, my house really did increase in value by $120,000 Nov-Jan but lost $60,000 in the last two weeks.
If you live in a zip code with lots of new construction Zillow won't give good results. Zillow looks at your last sale, assigns your house a percentage against the median price at that time, and then adjusts the value of your house based on the movement of the median sale price for your zip code. In my zip code, most of the new construction has been McMansions so the median price has gone through the roof, pulling up the Zillow values of the more modest houses with it. Now another subdivision in my zip code with more modest houses has reached the mushroom stage pulling the median price back down and thereby sending the Zillow value of my house plunging.
Zillow might work in a built out zip code but not here at the urban frontier.