Most people say auto-appraisals are crap. That is true of several online appaisers that substantially over-value domains. Estibot is pretty good at some domains, and not so good at others, but better than other auto-appraisals. If you use it judiciously as just one of the tools to help you form an opinion of a domain's worth, it's worth using. Each domain's value is different in different situations... even at the same time. What may be worth $100 to a domainer wanting "wholesale" pricing in a Domains Wanted ad, might be worth $1000 to an end-user looking for exactly what you have.