I've long wanted a feature that would allow me to set different wallpaper for different screens on my Xinerama system. At present, to use a graphic as wallpaper, it either needs to be tiled, or be set up to fit a 3000x1200 display (which means somewhat boring work in GIMP). However, KDE has announced that wallpaper can be selected on a per-screen basis with Xinerama. So this won't last much longer.
Well done KDE.