Comment 18 for bug 477256

A couple of more things I would like you to test in order to narrow this down (when booting without acpi=off)
- Could you try to disable desktop effects and see if you stil have freezes
- If you start the computer and leave it at the login screen, does it still hang, or do you have to log in first?
- Could you try a recent mainline kernel from http://kernel.ubuntu.com/~kernel-ppa/mainline/ (more info at https://wiki.ubuntu.com/KernelTeam/MainlineBuilds) and see if the new kernel makes the problem go away? The new kernel installs in parallel to the old one, and you can choose which one to start from the Grub boot menu (you can uninstall the test kernel after testing if you would like).