I believe the Displayport specification permits for daisy chaining of displays, so you could (if the hardware and software support it) drive two external displays independently from one port on the computer. I'm not saying the MBP or MB support it, but perhaps in the near future now that the 'books have two graphics "cards" (one card for the built-in LCD and one for the two external displays). Given how anti-port Apple seems, this would allow them to create a system capable of multiple external displays without adding a port.