I'm really not sure why this function wasn't made a part of Parser Functions from the beginning. It seems so basic. But thanks as always Bawolff, for giving the functionality in an extension. 19:31, 3 February 2012 (UTC)
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.