Have any of you directory owners used the meta robots=noindex,follow tag on pages for empty categories? If so, do you think it helped maintain PR on your category pages that did have listings? Did it hinder the SEs from indexing (non-empty) sub-categories of the empty cat pages?
I wouldn't reccomend it because people tend not to submit to non indexed, no pr categories. What I usually do is that as I add categories at my directory I also add an authoity site. Of course that slows a lot the growth of my category structure but it has worked ok for me so far