I submit to every free directory that requests submissions. It only takes a few minutes of time, and I see no downside to incoming one-way links.
I usually submit my sites to several directories each day. I submit to most all of the free directories as well as paid ones so long as I feel that the price is worth it for that particular directory. I agree that having many inbound 'one way' links as you can will help both in terms of PR and traffic.