One thing it doesn't cover (at least it didn't appear under T for Themes) is REMOVING themes. The software lets me manage themes - choose which are supposed to be visible if I let users choose and it lest me install them from files. How do I get rid of one so that it just isn't installed anymore? That'd be a useful thing to have in the wiki.
(Note: I did (in admin, themes management) click off all the older themes I don't want users to be able to select... yet when I looked at my own profile (admin user) for theme options, I still see all the old themes so something isn't doing what I expect...)
So if there's any info about getting old themes gone completely, I'd think a) I'd like to know it and b) it'd be a good FAQ inclusion.