I think it's a good idea in principle to let folks know the rules still apply here, both because we want to keep this thread around and because we don't want the kind of trouble that can bring a great thread to its knees. My only comment is that it's difficult sometimes to stay on the right side of the line between cautioning people and making them feel like they're being preemptively accused of something. I'm not saying your disclaimer explicitly does that, but it seems to assume everybody knows why it was placed there (this Diary thread, I'm gathering, was the one everybody's talking about). People wandering in who didn't experience the thread that inspired it might think it's a strange and somewhat foreboding addition and might not be quite as relaxed and chill in posting.
I'm not trying to be highly critical or anything like that. I'm just thinking about time when my friends and I (in real life! imagine that!) tried starting up a writing group, went overboard with the rules, and eventually everybody stopped showing up. Just so you know where I'm coming from.