It's funny to watch the cashier get offended when you call their "loyalty" program a "spy on what you buy" card. If the store was loyal to me it wouldn't shout my buying habits to every marketer around, so it must be there to keep me loyal to the store without any reciprocal loyalty.
Actually, the “loyalty” card thing is on the decline. Your purchasing habits can be traced through tracking of debit and credit card numbers.
I either don’t register my loyalty cards or give them bogus info.