Every day, hundreds of pre-owned domains are abandoned by their previous owners. Lots of those have got PR(page rank) because the previous owners promotion. When you buy these expiring domains, you get the PR as well. It is a short-cut to get a PR, as a newly registered domain will take some time and effort to get a PR. You may develop a web site with the PR domain or simply sell it for a profit. A highly after domain name is still hot property at the moment.  Carefully choose a meaningful PR domain, you may sell it for 100% profit or more.