I do not find it accurate for individual houses. It can be in the ballpark or way off. And I see inaccuracies in absolute price (listing things for 1/4 of what they'd go for, listing things as hugely more expensive than they'd go for) as well as the trends (for example, it says my house has gained $100k in the past nine months or so. My house has dropped in value during that time).
If you kind of look at all the houses in the various neighborhoods to try to figure an average, it won't be too far off, and you'll be able to tell which areas are pricey, etc.
It's best viewed as for entertainment purposes only.