They say once that you are listed in the Open Directory Project you will be listed everywhere else, it is also know as DMOZ. This is because the open directory project is handled by humans who hand pick the sites that are listed. Google respects this and often automatically adds the URL of a link that is picked to go into the Open Directory Project to its pages.
Open Directory is different than yahoo as it only performs WORD searches not KEY PHRASE searches. So much for your sophisticated keyword embedding techniques. So your description for OP should avoid pluralized words unless they are likely to be in search queries. On the plus side, Open Directory allows you longer descriptions than on Yahoo, but the category editor (who is very human in this case) may edit you down.
To apply go to the directory. Type a simple query that is likely to be used by someone searching for the contents of the page you are submitting. For example, if your site is lab diamonds try searches like "cheap lab diamonds" or "quality man made diamonds."
When the search results come back, the results will contain a small "category" subheading.
- After you've viewed the results of several searches and likely categories, click on the single category that you feel is most appropriate for your site. This link will take you to the category page.
- At the bottom of the category page, click on "Submit a Site". This will bring up the Open Directory submission form.
- Submit your site. All the usual techniques are appropriate. Make a note of the category you submitted to.
The "official" waiting period for Open Directory is 3-6 weeks. If you don't get listed within a reasonable amount of time a polite email to your category editor might speed the process along.