We don't allow blatant pimping of competing sites: as Tacks said, handling that privately and progressively has worked great for us.
In return, we do not pimp our site on competing sites. If one of our mods were to do, I would contact the other site admin and ask him/her to remove the posts and our mod would be removed from the mod status on our boards.
We do allow links in sigs to competing sites.
In the end, we feel we and our competitors will succeed or fail based on quality and communities and content. I'd rather spend my time making our place better instead of telling everyone how much better it is; people will notice the former and disregard the latter if there's no beef.
