For KDE users:
is usually enough for some settings (no "&" needed, it terminates directly). But not every setting is stored in ~/.nvidia-settings-rc - if you need other options then you need to use the direct commands. For special Twinview settings those are stored in xorg.conf in order to get active, that's not really optimal. Even fglrx is more flexible there.
mkdir -p ~/.kde/Autostart
printf '"#!/bin/sh\nnvidia-settings -l\n' > ~/.kde/Autostart/nvidia.sh
chmod +x ~/.kde/Autostart/nvidia.sh