I like being rewarded for things I already do.  I've been getting my car's oil changed at the same place for several years now, and a few months ago they introduced a loyalty program that makes every seventh oil change free.  I don't have to do anything different aside from remembering to have them punch a hole in my loyalty card.  I save money by doing pretty much nothing. 

The same thing happened at our local pet food store.  We've been buying a certain type of cat food for a little while, and one day a message showed up on our receipt that said we only needed to buy this cat food a few more times before we got a free bag of it.  We were going to continue buying it anyway, but it's nice to be rewarded for doing nothing.