Enable HiDPI mode in Mountain Lion w/o Quartz Debug
sudo defaults write /Library/Preferences/com.apple.windowserver DisplayResolutionEnabled -bool YES;
sudo defaults delete /Library/Preferences/com.apple.windowserver DisplayResolutionDisabled;
// by the way, you need to logout and log back in for this to take effect. Or at least that's what
// Quartz Debug says. Who knows, maybe it's lying?
// P.S. Go to [Apple menu --> System Preferences --> Displays --> Display --> Scaled] after logging
// back in, and you'll see a bunch of "HiDPI" resolutions in the list to choose from.