This was an interesting thread, I'm waking it up again since I've got an idea that wasn't mentioned yet.
But first: I did try gDevilspie. Unfortunately I couldn't get it to work, it seemed buggy (at least under Ubuntu 12.10). I spent some time on it but had to give up (I also couldn't find any documentation).
I had missed the link http://www.webupd8.org/2011/09/gnome...-start-on.html
before, just checked it out now. Haven't tried it yet.
That link and gDevilspie, if I can get it to work, could give me something similar to what I want, but maybe not quite.
My idea: I run a VNC server, and then for each workspace (or all but one) I connect with VNC to my own computer which would give me three dedicated "new" workspaces. I run the VLC viewer in full-screen mode in each workspace. Applications will be locked-in. Clipboard is shared. It should be light-weight, it should be fast.
There were suggestions up in the thread on running separate desktops, using "virtual jails (LXC?)" and others, but along with warnings that those solutions were probably hard to administrate and resource-intensive. And I'm not really a Linux guru (yet) so I don't think that would be the way to go for me.
But what about the VLC idea? Quite some work (for me) to set it up and get it working so I wanted to throw the idea out here first.