For me, it's value. If someone will go an extra mile for no charge, I'm likely to stay with the company, and probably pay for the same service the next time. I also always shop around for the best "bang for the buck."

I'm not sure about the "refer a friend" unless the coupon doesn't expire, etc. What is the point of getting $5 dollars off for referring a friend, when the coupon is for the service you've just had done? So unless it always applies to the next service, they are not an incentive for me. What about a coupon that applies to every new client? Or enter a draw to get a free mp3 player or something just by using the service, or for every referral?