specifically, for "incategory" and "deepcategory" (i.e., pages _not in_ category X)
also, would be nice to support "hastemplate"
often times, you want to find pages in category X which do not include template Y and vice versa.
as a side: we tried to build the "poor man's version" of this feature in hewiki years ago, and it didn't take. this implementation is way more usable, and i believe many users will find it very helpful. kudos!