Comment 12 for bug 212800

From what I've read it seems the Samsung bios ( > 09ST) is buggy and doesn't allow acpi to take over all the hotkeys correctly so the brightness keys still generate keycodes (repeatedly) and this seems to make X go weird (keyboard unresponsive, display sluggish).

Downgrading the bios to 08ST (using the information at https://wiki.ubuntu.com/LaptopTestingTeam/SamsungQ45) fixes the problem for me.