I've seen that Adbrite can change the adbrite code to Adsense code when there are no advertisers paying you. Is this allowed by Adsense? I'm just wondering, want to be completely sure.
Nope. I've had several emails from adsense support saying adbrite cannot be run on the same page as adsense. The contextual advertising is too similar.
funny there are alot of people have gotten emails that say there is no problem(including me). you can have adbrite and adsense on the same page and also you can have adsense in a banner rotation.