I found this article at www.seobook.com and thought it was worth sharing. It may be old news to some but certainly worth reading for those new (like me) to running a directory. Article: Web Directories...Are the relevant to SEO
That was a good read. It might be a good idea for some of the directory submitters to do an experiment like the one described in the article. Create a new site and only submit to directories (using their service, obviously) and study how well the site does in the three top search engines over 3-6 months. That would be great for marketing and would more likely make me want to use their service (if the results are good!).