Empty domain without any content, is going to lose PR in the future.
However, you can use relevant empty domain as an second entry point to your existing web-site.
Let’s show the example. I used to have lottery games site with lottery named domain (lotto-games.com).
I really do not care if that domain have any PR. However, historically this domain has lottery name and has been used, as a base for pure lottery content.
Have moved all the lottery content to the Best Games Directory. (link in signature). Instead of dropping lottery domain, I use it as an extra entry point to the whole lottery section, in Games Directory.
If you have good relevant domain (with some links and even small traffic) do not drop it. Just use it as an extra entry point for visitors, in the main section page or special landing page.