DMOZ was significant due to its extensive categorization and large number of listings and its free availability for use by other directories and search engines.
[6] However, a debate over the quality of directories and databases still continues, as search engines use DMOZ's content without real integration, and some experiment using clustering.
There have been many attempts to make building web directories easier, such as using automated submission of related links by script, or any number of available PHP portals and programs.
Recently, social software techniques have spawned new efforts of categorization, with Amazon.com adding tagging to their product pages.
Human-edited directories are often targeted by SEOs on the basis that links from reputable sources will improve rankings in the major search engines.
Some directories may prevent search engines from rating a displayed link by using redirects, nofollow attributes, or other techniques.
These directories are sometimes criticized due to long delays in approving submissions, or for rigid organizational structures and disputes among volunteer editors.
This method enables the directory to offer timely inclusion for submissions and generally fewer listings as a result of the paid model.