I did red/blue using the OpenGL accumulation buffer -- unfortunately this means it only works on nVidia graphics cards, since nVidia seems to be the only company willing to implement the accumulation buffer. But you could do it on other platforms using offscreen render targets.
From a software perspective, it couldn't be simpler to implement stereoscopic 3D. You set up the camera for the left eye and draw the scene, then you set up the camera for the right eye and draw the scene. My demo was extremely simple, just some gouraud-shaded spaceships flying around with a skybox in the background. But it looked fantastic, the things floated right out of the screen and into your face. :) Unfortunately, it requires red/blue glasses, and works best if you have a widescreen monitor and don't render to the edges of the screen.
A console implementation would require dedicated hardware. Not shutter glasses, as these induce eye strain and headaches. You need a visor with two small LCD screens. Small, high-resolution LCD screens are getting cheap -- the DS sells for $130. The barrier to entry is that every player needs one, and they all need fillrate. Fortunately, these won't be HD-resolution screens. 640x480 is probably the limit, so a GPU not much more powerful than the Wii could handle up to 4 players. I think you could actually launch a system like this with one visor in the box in the $299-399 range in 2011.
