Version:            (using KDE 4.1.2)
OS:                Linux
Installed from:    Fedora RPMs

Kwin does not support separated X screens. xorg.conf and Xserver is obviously OK, because  I can see Xserver cursor, I can run programs on second screen (but they are not manageable - because they does not has windows border, can not type or user mouse in them, resize, close .. so on)

Similar bugs for KDE3 was reported, I also tried to run kwin manually:
# DISPLAY=:0.1 kwin &
but it fails 

My configuration:
NVIDIA Driver Version: 173.14.12
GPU: nvidia Quadro FX 570M
KDE: 4.1.2
Linux: Fedora KDE 9 and KUBUNTU 8.10

PS: Xinerama works - very slowly and just a little bit (usually froze my desktop after some time - happen after I applied patch 4.1.1 -> 4.1.2 - I can run new appl. but can not use mouse and sometimes also type), but I do not want to use it, I have different LCD panels (laptop and desktop LCD) with different resolution and also I love when I can switch between virtual desktops independently on each screen (just hate I can't move windows between screens).