I found two very good articles, usefull for every diretory owner.
Directory Association?
First, I found on Aviva directory Blog. Aviva is one of the most known and quality directories I know. In their blog there is a proposition about creating a Directory Association. Read more about this interesting idea here.
Starting A Quality Directory
If you want to start a quality directory this article (from 2007) is something you MUST read. This article comes from authoritydirectory.com Blog and you can find it here
Tags: association, directory, quality, starting