Buy the book http://www.amazon.com/Ultimate-Question-Driving-Profits-Growth/dp/1591397839
Some more good examples of Net Promoter Score effect here.
There is also a Net Promoter Group on LinkedIn here.
Also check out http://www.netpromoter.com
It's easy to get an NPS of 100 if you only survey 5 people, how big does the survey sample need to be, more
Net Promoter Score Success Stories and Case Studies here
Good video on closing the loop here http://www.bain.com/publications/articles/closing-the-customer-feedback-loop-at-charles-schwab-video.aspx