Two things would really help me out with managing clients' use of categories.
Firstly, at the moment if you tick a sub-category it seems to be taken out of the heirarchy and that category appears at the top of the category list. This has been routinely confusing my clients as the hierarchy is no longer represented visually, making it hard for them to work out what is a sub-category of what. Even if a sub-category is ticked and NOT its parent category, it should still appear in the category list beneath it IMO.
Secondly, could there be an option to use radio buttons instead of checkboxes for categories? I have multiple sites now where having a post in multiple categories doesn't really work due to the way it's designed. Thus I need to stress the importance of only ticking one category to my clients, whereas it'd be much easier if I could just outright stop them doing it.
Hope these are taken into account as they're relatively minor issues, but make a huge difference to client usability from what I've seen. I've had a few 'well that's just a bit naff' type comments as a result of these niggles. :/