I’ve found myself recently adding lots of categories at a time, and it’d be a bit quicker if there was an ‘add another’ option on the category add page. So when you click that, it saves the current category entry and you get a nice clean form to add another one in, rather than being redirected back to the list of categorys in the chosen group.

This could also be useful in other places, for example when publishing lots of weblogs in succession.