A new setting found in Lion gives users the option to select a “HiDPI” resolution mode, which is believed to be similar to the iPhone’s Retina display. Current Apple displays do not yet support this extremely pixel dense resolution, but future notebooks and desktops may feature HiDPI. Like the Retina display, applications and graphics would have to be updated to look as crisp as possible on the higher resolution. It’s possible that the upcoming Thunderbolt display will be able to take advantage of HiDPI, but Apple has kept quiet about any such features. As noted by MacRumors, the actual number of pixels on a 30″ display could be around 5120 x 3200, while the resolution would remain at 2560 x 1600 (but double the density).
To check out this currently useless feature, enable HiDPI in the Quartz Debug application and view the OS X display options System Preference.