I spent some time testing the "live" version of iAds today. (iAds are now present in JourneyTag 1.0.7.)
First off, Apple is adamant that you not only hide the banner view when the ads can't load--but that you animate this hide action so it looks nice. I didn't think to much about this until now.
I noticed that viewing the same advertisement repeatedly without clicking, causes the the banner to hide itself off screen. I have theory: because the ads were already loaded, the normal "hide on error" behavior has more than one purpose. I think Apple will hide "loaded" banners if they think you've seen enough of them.
Second: As promised, you can view the ads without leaving the application. And you can even buy AppStore apps without leaving the advertisement or quitting your original app. Pretty cool!
Not only do the ads look great, but these little tidbits add up to a nice way to present advertising.