I second that, Cycleprincess.
No grunting, no flossing. And I think it's a universal truth that women are nicer to look at in the buff.
I'll add a rule, though.
No cell phone conversations.
SprocketMan - Doesn't your gym have a sign about kids over a certain age not being permitted in the opposite-gender locker room? (Perhaps you could suggest it.) Dang, that could scar a young girl... Our oldest is finally at the age where we need to reconsider the family shower concept. Sigh...