booting into live environment "as is" (both Unity and KDE) -- brightness keys don't work, brightness sliders in "settings" do nothing.
booting into live environment with "acpi-backlight=vendor" option -- in KDE brightness works as expected (both the keys and the slider); in Unity the keys produce "all or nothing" response, but the slider works correctly.
dell studio 1558, i3, intel graphics, oneric i386 beta daily build
booting into live environment "as is" (both Unity and KDE) -- brightness keys don't work, brightness sliders in "settings" do nothing.
booting into live environment with "acpi-backlight =vendor" option -- in KDE brightness works as expected (both the keys and the slider); in Unity the keys produce "all or nothing" response, but the slider works correctly.
too early to draw conclusions?
cheers,
alex