Our computers are still very much focused on the OS+app model, where you have an operating system and a selection of applications open. The organisation, if it can be said to exist at all, is taken from the "big pile, you sort it out" school of thought. It's up to you to remember what each app is for and what you were doing with it.
What if, instead, the operating system allowed you to set up different operating contexts, with collections of applications in each one, each with certain files open and certain settings relevant to that context, like "Research for Project A" with web browser tabs and note-taking programs, "Socialising" with chat and Facebook open and so on. Switching contexts is different to switching applications, especially when a task or project involves more than one program.
It could also be useful for contractors who have more than one job at any given time, and need to remember which documents and programs go with which client. To me, this seems like a more user-centric way of organising our machines, rather than making our mode of operation fit the machine's way of thinking.
Mokalus of Borg
PS - Sometimes I wish I had this.
PPS - I guess the OS vendors are too busy making things shiny to worry about productivity.