Hey SharkyB, hey caught up with you here from the tweets...

If you put the ads on a layer, you’ll want to watch out for transparent type flash ads.
Those have a way of finding there way to the foreground and that would push the entire content portion of the layout to the background. Just something to watch out for, if any of the ads will be flash expanding ads, etc.
I guess layers may not be necessary, just the top ad is basically an offset header, since the content areas are only at 800, the offset layer probably complicates things, nevermind... just thought it might make the flow of the layout easier to maintain.