Anybody interested in additional advertisement options for their games should check out ChartBoost. I was fiddling around with it today and managed to get it up and running in the next version of Pocket Ninjas in about 15-20min. They have a really detailed step-by-step on integrating it so its not too bad. Not sure what the returns are on it but since its not a banner ad (its an ad that pops up when the game first starts) it could work good along side with iAds.
Just a thought