dmoz, yahoo, or gump directory? They are just directories. No matter how hard it is or how much it costs to be listed, the fact remains the same. They are just directories. I don't know a single person that uses any directory faithfully to find what they're looking for. No directory is going to send even 1 unique site visitor every day, so I wouldn't rely on a directory for much of anything!
As far as
SEO is concerned, I focus on directories that consistantly rank high in the search engines when I am searching phrases that are related to the site I am working on ie... When I search using the phrase "widgets" because I sell widgets, I scan the first 3 or 4 pages of results for directories because theses directories will give you the best visibility. The rest of the directories have never done any of my websites any good at all.
I have never been able to get a site listed in the dmoz directory, and I have never payed the rediculous $300/yr to be listed in the yahoo directory and I still manage to get to the first page of results for my desired keywords/phrases.