On occasions some apps may seem to not adhere to the guidelines set by Apple. E.g. I get push notifications now and then urging me to buy some stuff. But that should not be allowed by the rules:
5.6 Apps cannot use Push Notifications to send advertising, promotions, or direct marketing of any kind
I also see way to many apps breaking the following rule on the App Store, but see nowhere to report them:
22.2 Apps that contain false, fraudulent or misleading representations or use names or icons similar to other Apps will be rejected