We use the Resources area similar to the Gallery but for documents, manuals, etc. on an automotive site. I'd like to help keep the category tree organized and to better do this I'd like users to be able to create categories. I may have a root category "Manuals" but I want end users that contribute to Manuals to be able to create categories for manufacturers as they add content. I can't keep up with all of the manufacturers that may get added so users need to be able to add categories as they contribute.