In this post in her Creating Passionate Users blog, Kathy Sierra suggests that we’re “better off thinking about ways to delight our users and customers (and employees and family members!) with a steady stream of Good Things rather than, say, giving them one big reward.”  She then hits on a concept I’ve blogged about before:

Too many companies seem to give all the cool toys and treats to prospective customers--like trade show attendees, for example--but completely ignore you once you actually BUY the thing! That's just 180 degrees wrong. If they're pouring all this effort into enticing new customers, I can't help but think that if they channeled more of that budget to their existing customers (through both having a great product and continuing to surprise and delight them after the sale), then they'd increase their sales and marketing force by an order of magnitude as those customers go out and evangelize with way more credibility than the company reps or ads will ever have.

What is your cost to acquire a new client?  Do you even know?  Are you spending at least that same amount on keeping each existing one?