For me, its a matter of preference. But I just want to make sure I don't miss anything. I see some sites with around 24 or more main categories and some sites with only about 14 or even lower main categories.
I agree it is a matter of preference to build the categories around the focus and reach market of your target audience
It is better to start with a small number of categories and gradually build up. Especially when your website is new, choose a tight niche and go from there.
I don't have any experience with structuring categories for a directory but from my experience with structuring content sites, I know that it is a bit of a nightmare if you have to change the structure later, so maybe it is better to start with top-level categories that are broad enough amd will stay the same forever, like Health, Technology, etc. and then gradually build subcategories, if you need to make the structure that diverse.
My websites are still newer but i decided to make space for new web directories as all my catagories were 5 Deep so i made some changes and add 0-9 A-Z so as to give room to all directories and thats 27 catagories added. http://www.biz-king.com/Computer/Web_Directories/ http://www.sleekdirectory.com/Internet/Web_Directories/ Do i think it will have an impact on the directory? Nah its just a matter of getting what you want out of your cliental, visabuility,and on a good PR page. thx malcolm