Retina MacBook Pro Can Run Three External Displays Simultaneously: Other World Computing posted this picture on their blog showing a MacBook Pro with Retina Display hooked up to a pair of iMacs serving as Thunderbolt displays and a third monitor via HDMI. This setup powers four screens with a total of 15,680,000 pixels.
The writer of the post, OWC Mike, seemed impressed with the performance of the MacBook Pro:
Moving images and media didn’t create any lag and we were able to play video on all four displays simultaneously.