Read original post at Mark Monster's Blog
Some of the things that are causing problems is the Ad Availability per Country. Depending on where your app is used more or less localized ads are used. So we know that the Microsoft PubCenter has a high eCPM for the US, it is low for The Netherlands. There are more of those problems with other Ad Providers. I heard there was a solution for this problem. Use the Ad Rotator for Windows Phone 7 which can be found on Codeplex. I did give it a try but at that moment AdMob was not supported (mostly because there were some AdMob specific problems) and also MobFox and Smaato weren’t supported. Those were the specific Ad Providers I was interested in.