For me, it's using notifications as advertising. Nothing pisses me off more than a lock screen full of "buy my new game" or "you haven't played me for 7 days, come back and buy my IAP" type messages. This is doubly true for games that, for whatever reason, don't honor the Notification Center iOS settings. I'll take a game off my device immediately for that. I know we have some prominent members that won't buy any games with consumable IAP. There must be other lines in the sand. What are yours?