I looked at Zillow when I was buying a house it was way off, not WAY off but enough off... then when you dig through the numbers, the Zestimate is nothing but an average of price modified with activity to try to reflect trending...
I think it's a neat site, as far as anything worth maintaining my traffic and care, there is nothing else there for me...
Propertyqube.com has a nice looking RE social network that has some features to keep me involved in the discussion with pros and home owners alike... it will be on that list soon enough.