Dmoz is also known as Open directory project(ODP). The listing of this directory is used by all the search engines and you get backlink from this listing which is really a highly authoritative one.
I think my niche, "limo service", has a shady moderator because it's been taking me 2 years and 3 month waiting time to keep applying to DMOZ and still no luck. I find it incredible that I follow their guidelines fully and I STILL can't get approved for Chicago limo service directory category after trying for nearly 2 years. And it's not like I resubmit after 2 weeks if I don't get approved. I give it ample time and my listing is very reasonable.
It is also an open project directory made by Netscape and Mozilla. Its a high authority directory and if your website or directory gets listed in this DMOZ site then search engine will count this site as a high authority website.
There are dozens of other issues to overcome before any site is viewed as an authority. One link from a site isn't even a factor.
It's a once great directory that's aging poorly due to lack of scalability of the volunteer model and frankly due to poor leadership from aol. I've got some pride of ownership there after years of being one of the faithful, but it is painful to look at the current condition and know it could have been avoided.
As TD says, it's a good link to have, but it isnt an SEO silver bullet. Was once, but the Google algorithm moved beyond that point. Maybe if that word gets out they wont get so much attention from the spam-prone.
Ten or more years ago DMOZ was a primary seed directory that most search engines used to discover new web sites. Today, search engines no longer need assistance in that area. As robjones who was one of the early DMOZ editors notes, it was a very important and useful directory at one time. That time has passed.
If you want to get a listing in DMOZ, follow the rules, submit your site and forget about it. There is probably a 90%+ chance that you will never get the link.
The following test was started in post #18 on September 10, 2011. As of today neither has been approved. I doubt if they will ever show up in DMOZ.