Wow. For the guys suggesting one post per thread, how exactly do you expect us to enforce that? There is no easy way to see how many times someone has posted in a particular thread. Even looking through the post history won't work because you can easily change the subject of a post to hide what thread you're posting in, not to mention that's too time consuming. Also all you'd have to do is delete the old post, since mods can't see deleted posts (and I suspect more than one of you who suggested this knew that).
Isn't that why there's the "Report to Moderator" link in the lower right corner of every single post, so we can bring a post to your (the MOD's) attention? If a pool/exchange/etc is spamming a thread with their service, then it should be up to the users to report said spam, to the MODS, then you can take action.
I think it would take up far less of your time for it to work this way, yes? I'm guessing right now, to in-force this rule you have to look at every new post on every thread to make sure someone isn't advertising. I'm sure your time could be spent doing much better things.
Does that sound like a good solution?