I am the main administrator of a wiki that could get a lot of mileage with Semantic Drilldown (http://dungeons.wikia.com). The only problem is the results returned do not seem to be a logical AND of the categories. Our category structure is organized like (3.5e/4e) -> User -> Class. The problem is that "User" and "Class" are subcategories of both 3.5e and 4e. When the drilldown category 3.5e and 4e is picked, then User and then Class, stuff from both 3.5e and 4e is showing up in the results instead of just the chosen main class (ie, if I pick 3.5e I still get stuff from 4e when I go all the way down to "class").
Description of how we do it: on our wiki, stuff in 3.5e has the categories "3.5e" and "User" and "Class" (all the categories) and "User" is a subcategory of 3.5e and "Class" is a subcategory of "User" and some other stuff. Pages appear in all categories from the root to the leaf.
So we really need an option to drill down with a logical AND on the categories. Preferably this option would be set in the control panel, because Wikia doesn't give us access to the back-end PHP files to set variables.