Previewed at WWDC, launching in the fall.
Microsoft Also Preparing for Desktop/Laptop Retina Displays
We'd previously reported that Apple had also been planning for ultra high resolution Retina displays in Mac OS X Lion. These ultra-high resolution displays would increase the number of pixels per inch found on both laptop and desktop displays.
There's been some doubts about when such displays will become commercially available, but it seems both Apple and Microsoft have built in support for it in their latest operating systems. Microsoft seems to indicate that they will be available within the next couple of years.