To be honest I'm not too excited about this. I don't want to relearn using a computer just to use a new operating system, and I definitely don't want to learn something that's completely different from the other OS I use on a daily basis.
I've used the Macs since day one, with the first MacPlus I bought.
What has happened is now nearly all document work is done on a smallish laptop screen as the laptops have gotten more powerful, and virtually even higher end software run on laptops just fine.
Over 20 years that has meant I, and many other Mac users, may keep 6-10 or more applications with documents open (Safari, Mail, MSWord, Excel, Acrobat, CAD, BBEdit) each with multiple windows open. It can be a mental mess to deal with. Likewise the Finder column views lead to some order, but when you get complex (30,000+ files), it can be hard to get to or find items even with Spotlight.
Viewing Solid Objects:
3D CAD systems have revolutionized the creation and visualization of objects for design & manufacturing, directly benefiting Apple in creating all its hardware, and Apple has lived that evolution. Pro Engineer, Unigraphics, SolidWorks, Ashlar and other 3D CAD have given an idea of how to allow concepts to be zoomed, rotated, and panned across a limited screen space so a user can examine an entire complex 'system' with a laptop, down to the smallest detail only a fraction of a thousandth of an inch if needed. (I use SolidWorks on a Boot Camped partition for my work)
I would not be surprised to see an ability to treat Application Arenas full of their documents and the Finder views become objects treated more like 3D CAD objects that lets a user resize (zoom), rotate into the next Appl. Arena, or Pan Sideways into a group of documents which are currently "off screen". If it is done right, I think it will be easily learned by those who have a need for complex work with many documents and applications open at once.
It is all about ease of use, recognizable objects, speed and consistency in allowing easier and faster work with less stress on the user: An Easy User Interface.
I think it is possible, and I know that the mechanical design guys at Apple (Including Ives) have lived with 3D CAD nearly their entire professional lives. Having used SolidWorks 3D CAD (& others) for 10 years, I think Jobs & Ives & crew have worked out the details of how to at least start this progression into manipulating virtual 3D views in a near intuitive way that makes computer use simpler, more logical and faster for the user.