Learned a lession this week with my app submission. I started suporting iAd on my app but forgot to include few extra validation when iAd is not available.
Here is the part of the doc from apple
"If you have dedicated a section of your app for an iAd, it's important to incorporate a banner view delegate that will handle common events, including errors," Apple says in the entry.
"Having the proper delegate to handle errors maintains the visual experience customers have with ads in your app by preventing a blank banner from being displayed when ads are not available."
Such strict measures will ensure consumers aren't faced with an ad network that appears faulty. Keen to make sure iAd retains its initial high regard, Apple believes some visual stimuli is better than nothing at all.
Cost: My one week of waiting time and missed iAd revenue :(