In our NPS self-improvement efforts we read a lot of literature on the intersection of social networks and marketing and especially we take note of studies that use data from mobile telephone operators. Why?
Because you can objectively determine who is in an "actor's" (customer) network and the relative strength of ties between customers. You can see who they call, how often and for how long.
NPS: Do detractors beget defectors? 3 Lessons learned from a 'customer churn in mobile' study