As the creator of a similar oscilloscope hack (the Terminalscope: http://hackaday.com/2010/02/24/oscilloscope-doubles-as-a-ser...) I find this very cool. If Craig is reading this, thanks for the shout-out :)

I'm not intimately familiar with the Game Boy's video signals, but I wonder: why the fancy microcontroller and digital-to-analog converters? The Terminalscope just uses a couple of op-amps to generate the horizontal and vertical sweeps. The microcontroller doesn't have to worry about moving the beam, so the refresh rate is very high and there's no flicker.

Maybe I should try this with my old Game Boy: the LCD is starting to die anyway...