The SEO value of a directory listing is relative. It is not something you should chase, but a positive side effect. Even the most reliable web directories don’t really give that “link juice” you hunt for when you get your site listed. So why should you list your website with popular directories anyway?
Believe it or not, although not relevant in terms of link juice, the directories might send you some traffic. Traffic is for the search engines a sign of relevancy (especially when it is targeted traffic). Listing your website in an authority directory, under the proper category, might boos your targeted traffic and that will give your website credibility in the eyes of the search engines. Targeted traffic increases the trust rank of a website.
For new websites directory listings are great for getting a site indexed, but this doesn’t necessarily lead to high search engine rankings. Plus that for a listing in an authority directory like DMOZ you have to wait up to six months, if not more. Besides, when you submit your site to DMOZ you have to make sure that the category is “active” meaning that it has a moderator. Otherwise you’ll stay in the queue and more likely never get indexed. And you’ll always wonder what have you done wrong. The answer is simple: you’ve done nothing wrong. It’s just that there was no one there to acknowledge your value.
In conclusion: while from a ranking perspective there is no real value in directory listings, you can only win from the targeted traffic they send, becoming in time a recognized resource in the eyes of the search engines.