Even with identical monitors, calibration is something you can never count on even if you are in the print graphics industry with specialized monitors and using spectrometers, calibration software, etc. Perception of contrast will also shift if playing in a dark or well lit room or if viewangle is not correct with some LCDs. Even contrast shift between the top to bottom of the screen can occur on some LCDs.
I like xplosys idea but you may want something where you don't allow the player to cheat the lighting in-game or are using scripts which would conflict.
I suggest having a menu screen image with a grayscale color bar and text instructing the user to adjust their monitor so that they can see all of the gradations (say, 10-15 grayscale blocks/swatches from 225,225,225 to 0,0,0 values) in order to play the game the way the game designers intend. This was done with some old survival horror game like Silent Hill or RE (can't remember).
Something like this...
It's far from perfect but should help if a monitor is tweaked really wrongly and clamping/blowing-out. If someone can adjust their screen to see all the gradation swatches and the game is still all black, then your game is probably too dark.
