For many businesses, the majority of marketing efforts are typically focused on generating new customers. While this is essential to business growth, it’s easy to overlook something just as important: retaining the customers you have.
According to an article in CEO World magazine, it costs five times more to acquire a new customer than it does to retain an existing customer. And existing customers can represent long-term revenue for your business, so it is important to understand the lifetime value of a customer to your business.
Read more - http://projectrev.com/2010/09/30/customer-retention-how-to-keep-the-customers-you-have/
edit