I'm newbee at directory managing, I just started a directory few days ago, I promoted it and I get incredible number of submissions, 600+/day. Very hard to manage, and create the new sub categories, I feel its getting confused, same sub categories in different categories and so on. It seems better to copy the categories and first level of subcategories from an existing directory. But which one is the best ?
Better to create a category structure that is unique to your directory and complete it prior to launch. Now you are getting hundreds of submissions to questionable categories and it sounds like you have a mess.
Just check those most popular directories like dmoz.org, yahoo directory, etc. Their category structures are the best.
I think the best way is to create your own detailed category structure. That way your site won't have the same content as everyone else.