We started out with 1000 pixels in a square metre and later bumped that up to 2500 to create the LED floor for the opening ceremonies of the Beijing Olympics. We added touch sensors which has got us to where we are now: an interactive floor with 25600 pixels in a square metre.
Interactive touch means your tech guy can program a Flash file with hot spots that react to mouse events and launch animated files to respond to someone walking or dancing across the floor. Much more simple than it sounds.
More information is available here: telematics.ca/gtek.