Well I guess you want to make sure it correlates with margins or...

Well I guess you want to make sure it correlates with margins or something else that is positive, but then you will not know what is cause and what is effect. I think I remember Telstra had some excitement about their NPS numbers at one stage, have you looked at that one for correlation by any chance? It may be easier to use the score by comparing similar businesses, i.e. Telco v telco?
My last dealings with Telstra (may have been a Vita Group store though) included a spiel from the sales assistant that if I didn't give all questions 5 out of 5s, he would miss out on his bonus - lol.
Good luck