This is disconcerting. In the bug report some people have nVidia cards - ATI and Intel, and all with the same problem. A lot of people affected and apparently Ubuntu responsible  have no idea what could be the problem. I'm using Kubuntu 12.04 64bits and I have a nvidia card:
01:00.0 VGA compatible controller: nVidia Corporation GF108 [GeForce GT 430] (rev a1)

and I can not detect what is causing the freeze. The final lines of kern.log I get are related always with "dri" and "nouveau" after the freeze:

======
Sep 23 20:45:43 yafupc kernel: [ 5981.225699] [drm] nouveau 0000:01:00.0: PFIFO: unknown status 0x40000000
Sep 23 20:45:58 yafupc kernel: [ 5995.352503] [drm] nouveau 0000:01:00.0: PFIFO: unknown status 0x40000000
Sep 23 20:46:04 yafupc kernel: [ 6001.512805] [drm] nouveau 0000:01:00.0: PMFB0_SUBP0: 0x037f0040
Sep 23 20:46:04 yafupc kernel: [ 6001.512811] [drm] nouveau 0000:01:00.0: PMFB0_SUBP1: 0x037f0000
Sep 23 20:46:50 yafupc kernel: [ 6048.184954] [drm] nouveau 0000:01:00.0: PFIFO: unknown status 0x40000000
Sep 23 20:47:50 yafupc kernel: [ 6108.196017] [drm] nouveau 0000:01:00.0: PFIFO: unknown status 0x40000000
Sep 23 20:47:50 yafupc kernel: [ 6108.196017] [drm] nouveau 0000:01:00.0: PFIFO: unhandled status 0x00800000
======
Sep 24 17:41:06 yafupc kernel: [24326.885728] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 24 17:41:06 yafupc kernel: [24326.885736] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 24 17:41:06 yafupc kernel: [24326.885755] [drm] nouveau 0000:01:00.0: validate: -22
Sep 24 17:41:06 yafupc kernel: [24326.888564] [drm] nouveau 0000:01:00.0: PFIFO: read fault at 0x000d7e3000 [PAGE_NOT_PRESENT] from PGRAPH/GPC0/TEX on channel 0x0001799000
======
Sep 25 10:59:45 yafupc kernel: [ 7205.739725] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7205.739736] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7205.739762] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7205.856639] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7205.856651] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7205.856673] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7205.875555] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7205.875567] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7205.875590] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7205.885346] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7205.885358] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7205.885381] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7205.914156] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7205.914168] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7205.914190] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7205.935033] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7205.935046] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7205.935067] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7205.940093] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7205.940111] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7205.940135] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7205.951218] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7205.951230] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7205.951253] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7205.971454] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7205.971466] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7205.971486] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7205.981017] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7205.981030] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7205.981052] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.000106] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7206.000118] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7206.000139] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.012955] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7206.012968] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7206.012992] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.033133] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7206.033140] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7206.033149] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.041898] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7206.041906] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7206.041914] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.054946] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7206.054952] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7206.054961] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.066027] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7206.066033] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7206.066042] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.077169] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7206.077175] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7206.077184] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.088264] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7206.088270] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7206.088279] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.099255] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7206.099260] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7206.099270] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.110403] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7206.110410] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7206.110419] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.124644] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7206.124649] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7206.124658] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.136181] [drm] nouveau 0000:01:00.0: fail set_domain
Sep 25 10:59:45 yafupc kernel: [ 7206.136188] [drm] nouveau 0000:01:00.0: validate gart_list
Sep 25 10:59:45 yafupc kernel: [ 7206.136201] [drm] nouveau 0000:01:00.0: validate: -22
Sep 25 10:59:45 yafupc kernel: [ 7206.136583] [drm] nouveau 0000:01:00.0: PFIFO: read fault at 0x000d052000 [PAGE_NOT_PRESENT] from PGRAPH/GPC0/TEX on channel 0x0001ac0000
Sep 25 10:59:45 yafupc kernel: [ 7206.136592] [drm] nouveau 0000:01:00.0: PFIFO: unknown status 0x40000000
Sep 25 10:59:45 yafupc kernel: [ 7206.136617] [drm] nouveau 0000:01:00.0: PGRAPH: TRAP ch 3 status 0x01000000
Sep 25 10:59:51 yafupc kernel: [ 7211.439193] [drm] nouveau 0000:01:00.0: PGRAPH: TRAP ch 3 status 0x02000000
=====================

I've tried many versions of the Kernel (ubuntu patched and mainline) and I always get the freezes. I think in my case the problem most often occurs minutes after waking from sleep mode. But I'm not sure. Currently use X swat PPA repository.
In my case, only the mouse pointer moves but nothing responds. Alt + SysRq RSEIUB works for me.
Could it be that the problem is related to a common problem with dri on all cards?