What do you do when a customer has a birthday?

Anaconda is an Australian based outdoor store selling clothing, boots and equipment for the various outdoor activities. When you purchase products they ask customers if they would like a 10% discount if they returned on their birthday and purchased something else. They provide a birthday discount certificate to existing customers. This is a simple, but effective promotion to get customers to come back by offering a discount for a one day a year, an example of the new trend of Perkonomics. I am sure this could be applied easily to other retail sectors.