What Defines a Satisfied Customer?

I was talking to my partner Dave tonight and, as our Saturday night chats are wont to do, we meandered into a few big picture ideas that affect our business. One thing we talked about was what defines a satisfied customer. One definition of a satisfied customer is someone who will continue to buy from you (or renew their subscription, if you’re in the on-demand market like we are). That’s a pretty minimal definition, but people don’t often think about having customers that are TOO happy. If they’re too satisfied, are you spending too much on that account? When do you face diminishing returns where the benefits accrued from high customer satisfication is not worth the expense to maintain such a strong relationship?