In general, the rules are too complicated, too confusing, and change too often. Other than award availability, that is why all the other problems arise. The key irritation is the failure of these programs to meet the traveler's expectations. They dangle a carrot to get your loyalty and then pull it away.

This is also why Southwest Rapid Rewards gets such high marks. The rules are simple, seats are available, and one's expectations are met 99% of the time. They don't offer or promise something they can't deliver.