Good idea
Well in order to make this extension work during preview it had to do some hacky things (Since pages aren't really in a category until its saved, during a preview its not in the newly added category, etc). The way it works around this is the best way i could think of, but its still a little icky, and would be frowned upon if this extension was being reviewed for wikimedia deployment, which is one reason this probably won't appear in parserFunctions extension anytime soon.
