MacBook Pro with Retina supports at least 4 screens
The Retina has 2 Thunderbolt ports plus 1 HDMI port. You can, in fact, plug one monitor into each ALONG with your internal screen… for a total of 4 monitors. Occasionally I’ll catch a bit of video lag in certain high motion situations (to be fair, the MacBook Retina was powering 11,404,800 pixels), but for a work Battle Station, it is fantastic. Theoretically, I could plug in 2 Thunderbolt displays into each Thunderbolt port (For a total of 4 Thunderbolt displays, 1 HDMI, and 1 internal, i.e. 6 screens) but I cannot confirm this… yet.