Sales, marketing and customer service - the holy trinity for customer acquisition and retention.  

All three are shifting ever closer to each other to the point that as Doug Kessler points out we'll look back and wonder why they were ever silo'd in the first place.  

SaaS companies are ahead of the pack in this convergence, they are already forging each operation closer and closer to focus their entire basis for activity around the customer.   The ones that get it right see explosive growth and retention. 

Ive seen both sides of this convergence first hand - the converged business always wins, and importantly, so do their customers.