Supposedly, they took only some of the features of WHS "Extended Drives" or whatever they called it back then (I never used that myself), and re-engineered from scratch making it available to both W8 and Windows Server 2012. So, under the hood, this should be a more solid and reliable server class feature than before.
Again, I never tested it directly yet, so I am not sure if, as I would expect, there are also different sets of features between the server world and the desktop world.

Indeed, if well designed, Storage Spaces could actually be useful in homes too, for the very reasons at the origin of the questions asked in this thread.

But with its current implementation (on paper) what leaves me very puzzled is that Storage Spaces lets you do things that are quite crazy to me, such as adding USB 2.0 drives to a pool of (e)SATA or SAS drives, for example, which can even make sense in some very peculiar situations if done by somebody aware of what is happening, but in most cases that simply means killing performances. I see that the idea in mind is plugging an external, USB based storage such as Drobo permanently (and still don't like it much), but I can also picture somebody doing such things and STILL treating USB drives as removable... Or, letting you add significantly smaller drives to a pool of larger disks, which would make no sense in most cases (all cases?).
I mean, on paper it is even TOO flexible if targeted also to homes, as it is. Nothing that would be dangerous for people in here - and all reversible stuff, I read - for example, but I can picture in my head so many friends who would just run into trouble or confusion for the simple reason that they would be acting according to the principle "add more drives to add more space" and plug an old 200GB drive to their 3x 1.5TB drives pool.

in any case, I have not even seen the GUI yet, other than in documentation.