I agree that you should delete people who join and don't post. send out a warning email just in case they are having a problem, but after a time, yes, delete them. they are no benefit to the board.
but keeping people from posting in all areas makes people feel unwanted or liek there under suspicion. instead, let everone post where ever and just watch them. its so easy to ban folks from a board. if enybody gets cought messing up, just ban them. then they can't come back.
just be tuff. only let folks in if you think you can trust them and if they break that trust, dump them. but if you could find something cute to put under our names ever time we get a certain amount of posts, that would be cute! maybe 100 posts=1 sparkly star...200 posts=2 stars..and so on. what do yoyu all think?