One of the most important component of search engine promotion is directory submission. Directory submission has a two fold benefit on a website, firstly, you get direct traffic, secondly the link from the directory (if its a dofollow link) helps boost your back links. If the directory in question is one of the top directories such as DMOZ, you get a lot of secondary links from other directories that get their feeds from DMOZ, this included Googled directory.
Directory submission is notoriously time consuming so clever webmasters have devised an automated directory submission service, the thing about automated submission is that it gets banned by quite a lot of directories so manual directory submission (time consuming and expensive) is the best way to get the most benefit from directory submission.