A directory is really only as good as the commitment of the owner. They're easy to set up, equally easy to neglect.
Free directories are great, the only cost is the time it takes to submit.
Paid directories need to be watched more closely - they can disappear with little comeback.
Never forget that the PR on the day you submit may not be the PR later on - it may riser higher, or slide into supplemental. There is no way you can keep track of all the directories you've submitted to without an automated system - and then is it worth the angst?
Many directory owners never move listings from the category they're submitted to, good ones will though as categories grown and require breaking into smaller pieces, re-titling etc. Automated systems need to be able to cater for this. Needless say I don't have a recommendation
