This is a mock up of proposed future Gnome Shell functionality which will take the concept of virtual desktops to a new level. Instead of being virtual desktops, they will be full desktops with their own files and background. The idea is that you will be able to work on different "projects" on their own desktop keeping files separate and minimising distractions.
I hope this is implemented as I think it's a great idea. Click the link for the full story.