Owning a few directories myself, this is a question that is of interest to me, especially after Matt Cutts recently stirred up some controversy when he invited people everywhere to report paid links as spam. With our directories, some listings are editorial while others are paid. In the beginning, every site added was editorial simply to populate the directory. Today we require payment for every submission simply to compensate for the time that is taken to review, edit and include the listing. Therefore the submitter is not necessarily paying for a link but rather paying for the editor’s time to consider the submission for inclusion.