Since 2 days (guess why) I’m the proud owner of a very shiny external monitor. Took a bit of effort to set up under Ubuntu (tip: don’t set the display to “not cloned”, and then try to run the external monitor at a different, high resolution than the local one — just keep cloning or shut off the local one and things’ll be fine :).
Anyway, I was running non-cloned, and it was nice, shiny and awesome-y resolution-y! But: if I closed the laptop, bam. Screen gone. It’s a power management thing. So we go to preferences > power management. Well guess what we can choose: shutdown, hibernate, sleep or blank screen. That’s right, no option to do nothing.
Luckily, there’s a hidden config option (see above link for explanation):
gconftool-2 --type string --set /apps/gnome-power-manager/buttons/lid_ac "nothing".
Yet another problem solved :)