Meh. I think they're kind of weak. Like, they're funny for a few seconds, but then the novelty wears off.
It seems like it would be funny if you could set up word filters so that only non-logged in people got the filtered words. Then you could swap words like fuck, kill, cum, etc. for words like hug, "high five", and "blow butterfly kisses" and stuff. Then, when lurkers read the boards they would think it was a cutesy love fest in here, only to find out how horribly wrong they were after they registered.
That would be awesome.