Comment 12 for bug 136853

Forwarding from a Ubuntu bug report by Martin-Éric Racine and confirmed by several others:
https://bugs.launchpad.net/ubuntu/+bug/136853

"After a few minutes of idle operation, the screen goes blank and cannot be returned to normal. The only way to get screen content again is to reboot, which is possible either by pressing the ACPI-enabled power button or a remote SSH connection. Broken DPMS is suspected, although I have no way of confirming this.

Purposely downgrading xserver-xorg-core and anything that depend on it, then pining it to that version, while keeping all the rest of the packages to Gutsy versions solves it, which suggests something related to X.org upgrade from 1.2 to 1.3 might be at play."

http://launchpadlibrarian.net/9095014/Xorg.0.log
http://launchpadlibrarian.net/9095015/xorg.conf

The same issue is seen in Ubuntu Hardy.