https://bugs.freedesktop.org/show_bug.cgi?id=41668
--- Comment #14 from dmotd inaudible@simplesuperlativ.es 2011-10-24 16:46:17 PDT --- (In reply to comment #13)
Try the following options in the kernel command line in grub: pci=nomsi noapic irqpoll and see if any of them help.
I have been running my machine with all the above kernel flags appended and i haven't yet experienced an issue. I haven't had a chance to exhaustively test these settings, but my machine has been active for a few days now without a screen lock, so I thought I would report back that this seems to help.