This worked for me aswell on my ASUS UL20a! I am very happy to see the community pull through with so much great info!
Thanks everyone for contributing these potential fixes, but unfortunately, I still don't have backlight control (or if I do, I don't know how to implement it). I just bought a Toshiba NB305 netbook, and am running UNR Lucid. I have tried installing the Toshiba laptop utilities, fnfx and fnfx-client, doing the two recommended modifications to grub (acpi_backlight=vendor; acpi_osi=linux) including changing the quote signs, and also aveminus' modifications to the /usr/share/hal ,,, file. Hitting the Fn-F6 or Fn-F7 keys still don't affect the brightness on my netbook.
I'm wondering if it has to do with the acpi_backlight=vendor line. Should the word, "vendor" be replaced with the actual vendor (TOSHIBA in my case)? Or is there some other way of changing the brightness besides using the Fn keys?
well, I still have this problem with the brightness keys under Maverick with an Asus UL30A. I have tried all the solutions named here but none works at all for me. With the first one, the brightness controls are still weird but now the don't "queue" and I can use the other Fn keys even if there are brightness actios (up or down) waiting...
I also tried with the 32 bits version, with Linux Mint, Lucid... and nothing new happens. I am thinking about installing Karmik because I have read that there it worked well. Is there any issue about UL30A+Karmik that I should know?
Meanwhile I find any workaround or solution I will keep the brightness at max...
The solution mentioned by golkran works for Acer Aspire 4736 with Ubuntu 10.04.
In /etc/default/grub, modify the corresponding line as,
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=Linux"
Just a quick thank you, solved my brightness control this way :D