Zillow is merely a real estate value estimator (they don't use sufficient data to earn the right to call themselves an appraiser nor do they provide sufficiently updated listings to justify calling them a listings service).
So sign up with Zillow and "claim" your home, then subscribe to email updates. You'll get mailed weekly with your "estimate". Using quotes there because, like gamblor956 says, the values are complete bullshit.
Zillow used to show percentage error but it was a web page showing inaccuracies by zip.
You are right that zillow used to show accuracy by zip code. But I am looking for more granular info.
Anyway, hope this post turns up some useful info.
Zillow estimate is way off by the way...