I think you hit the nail on the head.
The official word on that feature is that it uses your online storage space to save your Win8 settings which will then be retrieved the moment you log onto another Win8 desktop. That will make sure you always get your own desktop. Storage space which conveniently sits outside your common SkyDrive and which, so far, seems totally inaccessible to you.
Something which I consider to be very dubious. I mean; if /my/ data gets stored online why am I not allowed to see what gets stored? Heck; why can't I *remove* my stuff ?
Convenient is it that the moment you want to use their store and all that you'll have to sign in with your Live (now "Microsoft ID"). And all of a sudden all your stuff ends up on some mysterious part of the Internet.
And if only they managed to do a good job here, not even that!
When I started to test Win8 I used a dynamic Naruto Shipuuden theme on the desktop. Quite cool because it really showed how I felt (the picture with Naruto standing behind a fence of barber wire while he cuts his hand holding one of the wires): Imprisoned and incapacitated.
Dynamic... so other pictures are there too.
So; when the Win8 official release hit TechNet I gave that a try too. And amazingly enough; my desktop had the same theme and the same background as when I used the commercial preview. Out of the box. Yet only 1. My dynamic background had now turned static.
And the void? Well, that remained as vague as ever.
I think something really stinks here, and it aren't my feet.