why wouldn't you be able to game across them? you can set [strike]SLI or crossfire [/strike] with different resolution monitors if I'm correct
*edit: SLI or crossfire have nothing to do with the amount of monitors I just realise... I meant eyefinity or the like of course. I can understand that an FPS is not playable with 2 but racing games would work. Hell, there's real cars with a devided windscreen.