Where's your Warrior Card?

Today something from PF Changs came in the mail.  It resembled a Christmas card, but upon opening the envelope I discovered a letter thanking me for signing up for their Warrior Program. Affixed to the note was my personalized Warrior Card granting me 10% off the final bill every time I dine there.  Now PF Changs is all the way across town for me, but guess who thinks the drive just got shorter?

How can this be applied to your business?  Any restaurant can utilize this in similar fashion or at least have a punch card where the 6th time you visit is gratis.  Practically all service industries could look to implement this type of program.  How are you rewarding your loyal customers? Where is your Warrior Card?