This is a clever marketing ploy, but remember, by identifying yourself in this fashion ("Special cards", "Loyalty rewards") you are allowing the marketing department to build a big and valuable database on you and your activities, habits and preferences. They "pay" you in peanuts (Airmiles $20 spent= 1 reward point), and sell the profiles for huge sums to telemarketers, advertising agencies and other corporations anywhere on earth who express an interest and pay the price. It is like having a radio tracking collar around your neck.
As a guerrilla consumer, I delight in f*****g these data bases by borrowing and using other people's Airmiles cards and telling outrageous lies to market surveys. (The Albanian-Chinese family with six kids and a combined annual salary of $32,375 in my postal code area exists only in my imagination and about 5 marketing/polling companies... and if you work in marketing, you can guess if I am telling you the truth or not. ;D)
However, what started out as an amusing diversion has taken on more serious overtones when I realized that these profiles really do go anywhere in the world. When companies in China buy these databases, they are not just used in figuring out who wants to buy bycycles, but also feed their Intelligence organs. What exactly they can extract from this information is unclear to me, but why, after all, give them anything?
Use cash!