One of the side effect of overloading (perverting?) the WordPress category system to do tagging is you end up with over 1000 categories. The posting interface gets unhappy, and the
wp_list_cats template tag becomes pretty much useless.
(This post is another WordPress meta post, one of several I’ve got queued up in my head, and probably interesting to 3 people in the known universe, but here you go.)
better_cat_lists is WordPress plugin that adds a couple of more flexible methods.
wp_list_cats, but only categories with $cat_threshold posts in them.
wp_list_cats, but only from posts with the last $n days. You can also limit the total number with $cat_limit
Both methods use the same hack, they overload the
list_cats_exclusions callback to do positive match instead of the intended negative match – appending
and cat_ID in ($cat_ids) to the exclusion string. PHP at its finest, quick and dirty, like monkey patching but without language level support for it.