Latest updates from kde4.1.2 Factory seem to created an issue with kpowersave. Where Plugged in-Performance seems to fall back to Powersave setting screen brightness.
Actually though and strangely, the screen is dim at login. In kde3, once the desktop starts, brightness returns - so long as you are plugged in. In kde4 it just stays dim.
[edit]
I tried setting Powersave brightness to 100%
But still dim in kde4
Tried switching to Powerdevil for kde4 (had to remove kpowersave)
Same dim issue in kde4