Got similar symptoms (keyboard/mouse/screen freeze, screen keeps showing frozen image) on an AOpen Digital Engine 945FX

Running Lucid w/ latest updates as of 2010/6/18 (kernel 2.6.32-22). 

VirtualBox (non-OSE) is the only addition to this freshly installed desktop-i386 distro.  VBox was not running at the time of several of the freezes.

Since some folks were talking about wireless - this machine is wired ether only, no wireless hardware present.
Some folks were talking about filesystems:  Chose ext3 during the fresh install.
Video is using onboard Intel 945.

One freeze was during playing of a video in vlc - notably sound continued being decoded and played for several minutes after the visual freeze, until I cold booted.

So I made sure sshd was running after that, and so was able to ssh in and look at the system remotely during the next freeze.

Tried the DebuggingXorg gdb attach to Xorg - just got an eternal wait without return to gdb prompt at the attach.  Control+C did nothing during this wait.

Also tried firing up x11vnc to see if I could close things down cleanly or keep working after the freeze.  Another eternal wait after it tried to attach to the console session.

Found the following interesting messages via dmesg before sudo poweroff (which was able to shut the system down relatively cleanly, even to the point of reviving the graphics system and showing me the Ubuntu name and dots during shutdown).  They show i915 and Xorg tasks blocked on mutexes for > 2minutes, with backtrace.  Possible smoking gun for this class of freeze (looks xorg/Intel-gfx specific)?

[17520.270673] INFO: task i915:650 blocked for more than 120 seconds.
[17520.270679] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[17520.270683] i915          D 00000cdc     0   650      2 0x00000000
[17520.270690]  ef27def8 00000046 f68b2000 00000cdc 00000000 c0846740 ef249c4c c0846740
[17520.270699]  dbb92396 00000fce c0846740 c0846740 ef249c4c c0846740 c0846740 f6a0b880
[17520.270708]  00000000 00000fce ef2499a0 ef2e2414 ef2e2418 ffffffff ef27df24 c058a566
[17520.270717] Call Trace:
[17520.270737]  [<c058a566>] __mutex_lock_slowpath+0xc6/0x130
[17520.270742]  [<c058a485>] mutex_lock+0x25/0x40
[17520.270774]  [<f85ea2cf>] i915_gem_retire_work_handler+0x2f/0x80 [i915]
[17520.270782]  [<c016369e>] run_workqueue+0x8e/0x150
[17520.270798]  [<f85ea2a0>] ? i915_gem_retire_work_handler+0x0/0x80 [i915]
[17520.270802]  [<c01637e4>] worker_thread+0x84/0xe0
[17520.270810]  [<c0167740>] ? autoremove_wake_function+0x0/0x50
[17520.270814]  [<c0163760>] ? worker_thread+0x0/0xe0
[17520.270818]  [<c01674b4>] kthread+0x74/0x80
[17520.270822]  [<c0167440>] ? kthread+0x0/0x80
[17520.270828]  [<c0104087>] kernel_thread_helper+0x7/0x10
[17520.270859] INFO: task Xorg:1025 blocked for more than 120 seconds.
[17520.270862] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[17520.270865] Xorg          D 0000e204     0  1025    936 0x00400004
[17520.270871]  eda29e20 00203082 ed6c4000 0000e204 00000000 c0846740 eda4cf8c c0846740
[17520.270880]  d9b2130a 00000fce c0846740 c0846740 eda4cf8c c0846740 c0846740 ef132a80
[17520.270888]  00000000 00000fce eda4cce0 ef2e2414 ef2e2418 ffffffff eda29e4c c058a566
[17520.270897] Call Trace:
[17520.270902]  [<c058a566>] __mutex_lock_slowpath+0xc6/0x130
[17520.270906]  [<c058a485>] mutex_lock+0x25/0x40
[17520.270924]  [<f85ea220>] i915_gem_throttle_ioctl+0x30/0x70 [i915]
[17520.270950]  [<f81867cd>] drm_ioctl+0x25d/0x3e0 [drm]
[17520.270967]  [<f85ea1f0>] ? i915_gem_throttle_ioctl+0x0/0x70 [i915]
[17520.270978]  [<c01410f9>] ? update_curr+0x169/0x2a0
[17520.270984]  [<c016d4f5>] ? sched_clock_local+0xa5/0x180
[17520.270989]  [<c016aaaf>] ? __remove_hrtimer+0x2f/0xa0
[17520.270994]  [<c016ae38>] ? lock_hrtimer_base+0x28/0x50
[17520.270998]  [<c016bc86>] ? hrtimer_try_to_cancel+0x36/0xb0
[17520.271013]  [<f8186570>] ? drm_ioctl+0x0/0x3e0 [drm]
[17520.271021]  [<c0216231>] vfs_ioctl+0x21/0x90
[17520.271025]  [<c0216519>] do_vfs_ioctl+0x79/0x310
[17520.271032]  [<c0150ca0>] ? sys_setitimer+0x40/0x90
[17520.271036]  [<c0216817>] sys_ioctl+0x67/0x80
[17520.271041]  [<c01033ec>] syscall_call+0x7/0xb