Net Promoter Scores

I recently came across the concept of the net promoter score. It is beautifully simple - ask your customers the single question "Would you recommend XXX to a friend or colleague?" and you have a superb indicator of how your business is doing and a good predictor of revenue growth. You can see more about it here (a company set-up for conducting the research), here (for some research done by Bain & Co, here (for an interview Ogilvy conducted with a chap called Fred Reichheld or here for some research by LSE.