#1-Missing credits and the paperwork involved. Granted, I remember the "good old days" when you had to save your paper tickets and boarding passes for months, then submit them two or three times to get credited. But that was before everything was networked and computerized to the extent that it is today. Many airlines/hotel chains do it right. It seems NW and CO just can not be bothered to make sure that the credits post within a reasonable time, still.

#2-Deflating the value of your past loyalty by increasing award requirements or decreasing the seats/rooms available for award redemption.

#3-Poor customer service on the phone, at the gate, at the reception desk or other point of contact. No business can survive if they must constantly replace their most loyal and profitable customers, because of an employee who forgets that the customer is the one who actually pays their paycheck.