Both concepts have some good ideas, especially Zeitgeist. I think Zeitgeist could be very useful as alternative presentation mode in a file browser. GNOME Shell misses out on the crucial point in User Interfaces: making working with the computer easier for the user.
I have set up my system for "side-by-side" viewing and editing of documents. I use workspaces (virtual desktops) to keep the windows that I use for a specific project together. What I would like is to tune a workspace, so that the file browser shows the project files as default, the webbrowser comes up with a project-specific bookmark bar and the applications that are needed for the project have their icons. It should be possible to save (and freeze) the workspace state independently from the other workspaces on the system.
Bonus points when you can make the e-mail client "workspace sensitive" and give it a button that loads the relevant workspace for the email.