Comment 41 for bug 505452

There exists a patch for the main kernel, but it has be rejected, due to non-technical reasons...
https://patchwork.kernel.org/patch/61816/
The reason for all these issues are also mentioned there.

Short summary:
The ASUS BIOS firmware is evil, because it sniffs, which OS is running. In the past Linux identified itself with "acpi_osi=Linux". But the newer kernels don't identify themselves. The ASUS firmware changes the ACPI configuration according to the detected OS and since it cannot detect "Linux" anymore all ACPI features go wrong.

Either ASUS updates its BIOS, Ubuntu devs include the mentioned patch or you have to change the GRUB configuration yourself.

For this you have to edit your GRUB configuration at "/etc/default/grub" and change a line:
GRUB_CMDLINE_LINUX_DEFAULT="quiet acpi_osi=Linux"