Directories - why use them?
Directories offer two great factors:
a) Traffic - people browse directories and this will lead to some click through traffic to your site. There are 100s of directories so a reasonable flow of traffic can come from directories.
b) Improved Search Engine Rankings - directories are a source of ONE WAY links (much better than reciprocal links). Choose Directories with page rank - the higher the better! Lots of high quality incoming links will help your search engine rankings. NB - it is important to get links from a variety of sources - not just Directories.