When I set the display resolution to 1366x768 on my ubuntu 12.10 desktop (which has nvidia-current drivers installed) the next time I boot, I can't see the lightdm login screen (the monitor displays "no signal"). This is mainly because I use a wall mounted television as the monitor, and it supports only some very specific resolution. The same happens with 1360x768. Both resolution work perfectly on a logged in ubuntu desktop. Just not the lightdm. The condition was similar in ubuntu 12.04 but it worked perfectly in 11.10 and 11.04.