Movable Type 3.0 won’t have subcategories, and David Raynes’ SubCategories does not screw up the basic database structure, so I took the plunge and put in subcategories on this site. You can see them; they’re the indented smaller categories in the category listing on the right.
If you look at the Gaming category, say, you get to see all the entries in Gaming and in the subcategories of Gaming. If you look at Game WISH, you only see the Game WISH entries. This suits my organizational nature.
I am still fiddling with the navigation on the category archive pages; it’ll likely change again at some point. I may tweak the top level category navigation as well. Suggestions are certainly welcome.