Forwarding this bug from Ubuntu reporter Stuart Langridge:
http://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/768184

[Problem]
Infrequent gpu lockup on i965.

We've had a handful of reports in the last couple weeks of a gpu lockup on i965 systems which had not had freeze troubles for a long while (>6 months).  Most reporters have experienced the freeze only once or twice; they don't know how to reproduce it, nor really have a way to definitively tell whether it is fixed or just occurs rarely.

I'm forwarding this report on the chance that the bug is a recognizable one to upstream; I don't think users are going to be able to pinpoint this down any further.

Bugs I believe to be dupes, all on i965 systems:

768184  IPEHR: 0x01800020
767511  IPEHR: 0x60020100
767425  IPEHR: 0x08000000
757968  IPEHR: 0x14000000

These i965 reports started coming in shortly after when we updated Ubuntu from xserver 1.10.0 to 1.10.1 and mesa from 7.10.1 to 7.10.2 and adding patch 25521900d to -intel (bug #35808).  (Due to the intermittency of the bug I haven't had people try downgrading those packages.)

[Original Description]
Crash which required reboot. The crash itself is described in https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/768176 and this is after I persuaded apport-gpu-error-intel.py to run.

My screen went entirely black (both laptop screen and second monitor). Switching to a VC did not show anything on screen. At first I could still hear sounds from running applications, but eventually (after ~10 seconds) they stopped. I had to powercycle the machine to get control back. The "system problem detected" apport dialog offered to let me file a bug, but then I got another crash dialog saying "apport-gpu-error-intel.py closed unexpectedly".

ProblemType: Crash
DistroRelease: Ubuntu 11.04
Package: xserver-xorg-video-intel 2:2.14.0-4ubuntu7
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic-pae 2.6.38.2
Uname: Linux 2.6.38-8-generic-pae i686
Architecture: i386
Chipset: i965gm
CompositorRunning: compiz
DRM.card0.HDMI.A.1:
status: disconnected
enabled: disabled
dpms: Off
modes:
edid-base64:
DRM.card0.LVDS.1:
status: connected
enabled: enabled
dpms: On
modes: 1280x800
edid-base64: AP///////wAwZAYjMjQ5NTISAQOAHRJ4Cof1lFdPjCcnUFQAAAABAQEBAQEBAQEBAQEBAQEBKhwAqFAgHjAQMCIAH7QQAAAYAAAAAAAAAAAAAAAAAAAAAAAAAAAA/gBSUDc3NKMxMzNFV0REAAAA/gAIDBAUKFB/2AEBCiAgAL4=
DRM.card0.VGA.1:
status: connected
enabled: enabled
dpms: On
modes: 1680x1050 1280x1024 1280x1024 1280x960 1152x864 1024x768 1024x768 1024x768 832x624 800x600 800x600 800x600 800x600 640x480 640x480 640x480 640x480 720x400
edid-base64: AP///////wBMLdIDMjJBSCMTAQMOMB54KtxVo1lIniQRUFS/74CzAIGAgUBxTwEBAQEBAQEBITmQMGIaJ0BosDYA2igRAAAcAAAA/QA4Sx5REAAKICAgICAgAAAA/ABTeW5jTWFzdGVyCiAgAAAA/wBIOUZTODM5NDg1CiAgAAI=
Date: Thu Apr 21 10:25:20 2011
DistUpgraded: Log time: 2011-01-18 17:25:59.814253
DistroCodename: natty
DistroVariant: ubuntu
DuplicateSignature: (ESR: 0x00000001 IPEHR: 0x01800020)
ExecutablePath: /home/aquarius/apport-gpu-error-intel.py
GraphicsCard:
Intel Corporation Mobile GM965/GL960 Integrated Graphics Controller (primary) [8086:2a02] (rev 0c) (prog-if 00 [VGA controller])
Subsystem: Dell Device [1028:0209]
Subsystem: Dell Device [1028:0209]
InterpreterPath: /usr/bin/python2.7
MachineType: Dell Inc. XPS M1330
ProcCmdline: python apport-gpu-error-intel.py
ProcEnviron:PATH=(custom, user)
LC_MESSAGES=en_GB.utf8
LANG=en_US.UTF-8
LANGUAGE=en_GB:en
ProcKernelCmdLine: root=UUID=b572742c-deea-43ec-92d3-b1d1e6b6802f ro quiet splash
ProcKernelCmdLine_: root=UUID=b572742c-deea-43ec-92d3-b1d1e6b6802f ro quiet splash
RelatedPackageVersions:
xserver-xorg             1:7.6+4ubuntu3
libdrm2                  2.4.23-1ubuntu6
xserver-xorg-video-intel 2:2.14.0-4ubuntu7
SourcePackage: xserver-xorg-video-intel
Title: [i965gm] GPU lockup (ESR: 0x00000001 IPEHR: 0x01800020)
UpgradeStatus: Upgraded to natty on 2011-01-18 (92 days ago)
UserGroups: adm admin cdrom couchdb dialout dip floppy fuse lpadmin plugdev video
dmi.bios.date: 12/26/2008
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A15
dmi.board.name: 0N6705
dmi.board.vendor: Dell Inc.
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvrA15:bd12/26/2008:svnDellInc.:pnXPSM1330:pvr:rvnDellInc.:rn0N6705:rvr:cvnDellInc.:ct8:cvr:
dmi.product.name: XPS M1330
dmi.sys.vendor: Dell Inc.
version.compiz: compiz 1:0.9.4+bzr20110415-0ubuntu2
version.libdrm2: libdrm2 2.4.23-1ubuntu6
version.libgl1-mesa-dri: libgl1-mesa-dri 7.10.2-0ubuntu2
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 7.10.2-0ubuntu2
version.xserver-xorg: xserver-xorg 1:7.6+4ubuntu3
version.xserver-xorg-video-ati: xserver-xorg-video-ati N/A
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.14.0-4ubuntu7
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20110107+b795ca6e-0ubuntu7