There does seem to be disagreement over whether directories are worth submitting to. But from my experience it's worth doing.
And it does seem to work better for Yahoo. I was promoting a new site recently, and after about 20 directories submitted I was on page 5 for a certain search term. A week or two (and another dozen or so submissions) later I was on page 2 for that term. So they definitely help. Google and other search engines seem to be harder to crack.
I'd say the best approach is to get the young, free ones because a certain proportion will become high PR sites and you'll have a link there forever. But to make sure you get some of these you have to submit to heaps and heaps of them, of course.