We are digging into cocos2d for several new projects (Hyper WARP II, Legends of Hylore) and wanted to try out the new iAd's. So we built an app for viewing some very cool particle displays and added iAd's to it. You can read more about it HERE and once it has been approved by Apple we'll update the page with a handy link.
We will also be clearly marking which apps require iOS 4 with this handy image.