They are a pain. They make the window jump all over. It does make me spend less time on the board when they get in the way. So, from that perspective it's not so bad.
I think the site admin has control as to whether these appear. I'm on other forums and they don't have the pop ups. I haven't paid attention as to what they are advertising. If its the same company then I'm thinking it's what the admin has agreed to.