Comment 80 for bug 1007765

Adding 'acpi_backlight=vendor' to the GRUB_CMDLINE_LINUX_DEFAULT options in /etc/default/grub (comment #71) also worked for me. 'quiet splash' and 'pcie_aspm=force' options shouldn't be necessary in this situation (though 'quiet splash' is added by default). Also, as a general rule, you should check what commands do before blindly following solutions followed by others. Google is your friend. ; )

$ uname -a
Linux Mazinger-Z 3.5.0-22-generic #34-Ubuntu SMP Tue Jan 8 21:47:00 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

$ sudo lshw -class system
mazinger-z
    description: Portable Computer
    product: Inspiron N5010 (To be filled by O.E.M.)
    vendor: Dell Inc.
    version: A04
    serial: 1D04FL1
    width: 64 bits
    capabilities: smbios-2.6 dmi-2.6 vsyscall32
    configuration: boot=normal chassis=portable sku=To be filled by O.E.M. uuid=44454C4C-4400-1030-8034-B1C04F464C31