There are two important directories which are DMOZ and Yahoo. Google can not be considered as a directory. Google is a search engine. The difference between directories and search engines is that directories file each site under categories and sub categories. Because the search engines seems to be hype and the online marketers seems not to recognize the essential parts of directory submission. Directories focus on listing sites so that the users can find the links under the categories. Search engines spider the website and if a site offers well optimized keyword pages it will get ranked. And the search engines have a commercial intentions to attract the potential customers.
There is the possibility to submit the sites to a directory manually or automatically. After the submission a person of the directory will review the link and either it gets approved or rejected. One of the main advantages of directory submission is that the search engines will crawl the directories for new links and will index the links which the spiders finds valuable. This will eliminate the time consuming task of submitting sites to search engines.
The advantages of directory submission are: It gives you one way link. Directories allow the people to create anchor texts and insert the targeted keywords. Mostly the website directories are free of charge. For Targeted traffic website directories are ideal.