Is there any restriction or guideline for how long and how frequently an app can display an iAd and still be approved? Would it be acceptable by Apple’s terms if one was to make a game which displayed an iAd at the top of the screen through all gameplay?
There is an amount of time an ad must be displayed before changing to another ad, I think it is 2 minutes. You cannot refresh every second for example to get more hits. But no restriction on displaying ads at all times.
"Once you display the ad banner, you should leave it visible for at least 30 seconds, unless the user requests a new page or screen as described in your agreement under “Minimum Rendering Time”.
Error Handling
If an error occurs, the banner view calls the delegate’s bannerView:didFailToReceiveAdWithError: method. When this happens, your application must hide the banner view."