Comment 239 for bug 568611

Backlight brightness control in Ubuntu 11.10 (Oneiric) -- summary of known remaining issues:

As noted previously, some Ubuntu 11.10 (Oneiric) systems will still need to boot with "acpi_backlight=vendor" or some other vendor-specific boot parameter to make the brightness up/down keys work.

Screensaver blank screen gets stuck off: In Ubuntu 11.10 (Oneiric), users of Dell Studio 15, Dell Studio 1558, and some other models may experience the problem LP: #872652 ("screensaver backlight stuck off, system looks hung"). If you find that your backlight gets stuck off when the screensaver blanks the screen, see that bug number for the fix.

Some (all?) systems with Intel GMA4500-based graphics processors have their brightness controls "inverted" such that the brightness-down key increases the brightness and vice versa. This also results in the system starting with its brightness set to minimum (or even "off") when the system first boots. This problem is tracked by LP: #752165, LP: #765438, LP: #773471.