Currently, such displays are prohibitively expensive in sizes much bigger than a phone, but they won't stay that way forever.
So Apple is building support for the inevitable Retina Display laptops into its upcoming OS X Lion. Referred to as "HiDPI display modes," the change would allow the OS to quadruple the resolution of an app but keeping everything the same relative size. It's much like the resolution scaling that the iPad does on non-native iPhone apps.
Sure, there aren't any 13-inch screens that exist with the 2560x1600 resolution to make this possible. Yet. But there will be, and that is exciting.