Hello,
I found it to be way off in some areas, for example, in SLC it identified a property as being worth $1.2 milllion, the property was purchased a year earlier for $200k. In some other areas I found it to be off by as much as 20-30%. Suprisingly my home in San Diego was fairly accurate. I think as they collect more data the accuracy will increase, however it will still be an issue in sdome of those non-disclosure states like UT and TX.