I'm not complaining, and the site need to make money, so this is not a criticism of the ads, but I noticed some unusual functionality with them:
If you are not logged in, the vertical banners can be collapsed. If you're logged in, they can't be collapsed. In fact, if you're logged in, there's a space reserved for the expanded banner even if there is no banner being displayed - just a blank space to the left of the forum content.