[MetalMilitia]

Yeah I think the only game I've ever played across both screens was Supreme Commander as it was an officially supported feature (you'd get your main HUD/map on one monitor and then another map on the other which you could zoom into as far as you wanted. This way you could have your base always shown on one monitor and whatever else on the other - it was really cool, just a shame I didn't like the game much).

As others have said it doesn't work with shooters because of the inch of plastic right where your cross-hair is.

I really wish more developers would start adding support for a second screen to their games. It'd be so useful to just have a map or inventory permanently displayed on your spare screen.