As a directory owner I use other directories to promote and build links. With two general directories I undertook different paths. Directory 1 was submitted to thousands of free directories, as well as paid directories, heavily social bookmarked and promoted in other ways with the result that it has hundreds of backlinks.
Directory 2 was submitted to about 20 paid directories that I judged to be of good quality and with a fairly high PR but little else in the way of promotion.
Both are now PR4.
A properly managed general directory really is just a series of niche directories.