If game makers take up this approach in force, that will be a fair sight better than the status quo of supporting "free" games by way of in-app purchases (that are essentially mandatory to get the full experience of the game).
This is why we've never touched it. On Facebook, we just have to make our users want to invite other users. We don't have to constantly release new versions and incentivize users to download them just to get ourselves back in the top 20. There are some tricks, of course, but they're less of a detour from the desired path, if that makes sense.
iAds will make success on the platform a numbers game. Every free app will run it because it can't pay worse than the current options, even with the 40% rake. Paid apps will break out the spreadsheet and almost certainly find a CPA below the app's price for a paid one. My totally off-the-cuff guess is that with a really engaging iAd you'll end up paying $1 to sell a $2 app, at which point it's all about volume. Selling a million like that might be doable, and now we're talking money in line with what Facebook apps can make.
Still, the problem will be that the most successful iPhone apps make about the same amount lifetime that the most successful Facebook apps make in a month. But the odds of succeeding may now be high enough to make it a worthwhile play.
Maybe the App Store needs iAd/GameKit integration of a 'like'/'recommend'-to-friends feature.
Still, I imagine if Apple made an opt-out method of automatically friending all of your email contacts who have iPhones (or at least an opt-out method of seeing them) it would be popular.
Actually, I'd probably be influenced more, since I know some Facebook games force you to recommend it in order to get access. But if this game center, like XBox Live, can just show me what my friends are actually playing... that's the best endorsement they can give me :)