Conventional wisdom holds that the customer is always king (or queen), but not all customers are created equal, write authors Selden (a consultant) and Colvin (a Fortune editor-at-large); in fact, some may be hurting your business (e.g., people who phone customer service lines thousands of times in a single year). So, they argue, it's smart strategy to figure out which customers are most valuable to you, and to lavish your attentions on them. The authors point out a number of companies that are reorganizing how they operate, like Best Buy and Toronto-based Royal Bank. The tone is exceedingly businesslike; sans colorful narratives or rhetorical flourishes, the authors march stiffly through the points they want to make. It's unclear sometimes how behavior should be altered by this philosophy: should you, for example, refuse to do business altogether with unprofitable customers? But the book's central thesis manages that rare mix of being both surprising and eminently reasonable.