If I remember correctly, for some strange reason, if you use kde with gdm, or gnome with kdm, you don't get the "poweroff" or "reboot" buttons.
Reference: XGL HOWTO (lost the link) -- No shutdown option (button) visible https://launchpad.net/bugs/50471 -- kubuntu-bugs mailing list kubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/kubuntu-bugs
