I’ve pretty much completed implementing the mechanisms in nautilus and gnome-settings-daemon to implement per workspace wallpapers. I’ve created a short video that shows the current state of the functionality:
As you can see the wallpaper is currently set for whichever workspace the appearance capplet is on.
I’ve put most of the patches (except the gnome-control-center one) into bugzilla:
gnome-control-center patch is available here: http://git.jsharpe.net/ but is still a work in progress.
I’d appreciate feedback on the patches.