Keep your enemies close, but customers even closer is a really interesting article at Observer. The article starts like this:
Despite what they say - and often even think - many, perhaps most, companies are surreptitiously at war with their customers. Through nuisance games, dirty tricks and small print they take every opportunity to extract more from your wallet for no extra service.

After much experiment, Fred Reichheld (director emeritus of consultancy Bain) and Satmetrix, a company that focuses on measuring customer experience, boiled it down to a single question: on a scale of 1 to 10, would customers recommend the product? Customers who rate the product 9 or 10 are ‘promoters’; those who rank it 0 to 6 are ‘detractors’. Subtract the percentage of detractors from the percentage of promoters and you get a ‘net promoter score’, or NPS.

Some additional links:
Net Promoter official web site
Net promoter score at Wikipedia

The solution sounds easy but I wonder how many companies that dare to introduce their NPS-method.