This article was written from an SEO perspective and is aimed at the domain buyer, so it isn't all relevant to those here, but it is an interesting perspective. If noting else it does help you understand your buyers better, and that's always a plus.
http://thedigitalelevator.com/seo/domain-name-value/#domainnamevalue
http://thedigitalelevator.com/seo/domain-name-value/#domainnamevalue