I found this study of Leveraging Customer Feedback to Increase Loyalty very insightful. Please note particularly:
In a large field experiment with highly satisfied customers of a Fortune 500 firm in the hospitality industry, the researchers track both customer attitudes and behavior over a 12-month period. The researchers find that a firm response to highly satisfied customers (in the form of a “thank you” email from the restaurant group’s president) increased patronage by more than 50%. In addition, it significantly strengthened the communal relationship with female customers.