Comment 8 for bug 872932

I can confirm both the alternating behavior with Fn Up Arrow as well as the not restoring full brightness when I swipe across my Dell Latitude D620 trackpad.
https://answers.launchpad.net/ubuntu/+source/acpi/+question/174296

I think it is in Gnome upstream of Ubuntu as this occurs on Fedora 16 (but not F15) Gnome:
http://ask.fedoraproject.org/question/121/laptop-screen-dims-on-f16-unlike-f15
And not on Kubuntu or SuSE 12.1 KDE.