Comment 22 for bug 439137

If the jaunty kernel has the same problem, that's an interesting finding, thanks! So the next thing I'd like to try is to check if one of the udev probing programs causes this. So let's disable as much as possible (but let the system still boot):

  cd /lib/udev/rules.d
  sudo mv 60-cdrom_id.rules{,.disabled}
  sudo mv 75-cd-aliases-generator.rules{,.disabled}
  sudo mv 95-devkit-disks.rules{,.disabled}

Then please reboot and see if you can mount CDs manually (sudo mount /dev/sr0 /mnt) and if blkid works again (blkid -p /dev/sr0). If it now works, then we scored! In this case, please rename the rules above back from .rules.disabled to .rules one after another to find out the culprit.

If it still doesn't work, I'll attach a stripped down 60-persistent-storage.rules which will avoid touching the CD.

   sudo cp 60-persistent-storage.rules{,.orig}
   sudo cp /where/you/downloaded/60-persistent-storage.rules .

and the same reboot/test cycle again.