At the Other World Computing Blog, a photo shows the demo setup: the MacBook Pro with Retina Display connected to two Thunderbolt-enabled displays (in this case, two big iMacs at 2,560-by-1,440-pixel resolution) and a computer monitor connected with HDMI (at 1,920-by-1,200-pixel resolution).
The new MacBook's video power and Thunderbolt technology must have helped performance.
Moving images and media didn’t create any lag and we were able to play video on all four displays simultaneously.
Of course, the quality of what's showing on the screen can vary depending on whether the application has been updated to support the Retina display's 2880 by 1800 screen. Apple updated OS X Lion and Mac applications such as Aperture, Final Cut Pro, Mail and Safari.
The Verge has a great photo showing the side-by-side comparison of Safari and the non-Retina-savvy Chrome browser. You can see how the text looks blurry on Chrome. Check it out.