I've just installed Ubuntu 9.04 on my Acer Aspire 4810Timeline. Everything seems to be working ok, except for the screen brightness. The [Fn]+[Up]/[Down] combination displays the popup and the bar is moving correctly, but the brightness remains the same. I've checked the contents of /proc/acpi/video/OVGA/DD02/brightness which changes accordingly. Anyone who's had the same problem, and knows how to solve it?