Suggestion: if I type something in a category box and it's not a category yet, ask me "Would you like to create a new category for XXXX"?
This would prevent many categories from being created by mistake (usually either a typo, or if by mistake I typed a tag's name into the category box). It would add one more click for the rare occasion when I actually want to create a new one, and save many many clicks for each time I create a category by mistake and then need to go to dig into the settings delete it.
Thanks for your consideration!