depends on the length of the domain name and if the name only relates to a specific niche or is general, numbers or dashes also decrease the value
Apparently an aged domain name is what gives most of the value, not necessarily the PR rating. PR ratings can drop whereas the age is always there.
I am afraid especially if many members are not aware of the fact that this trick is no longer going to work. Google is now a registrar with official access to the whois database. Any attempts to buy a years old domain will not be worth anymore because google will now also monitor the registrant history. And frankly speaking, I never give any importance to PR. Please clear your doubts with this article http://www.free-seo-news.com/newsletter213.htm#facts