I'm previewing Windows 8 as well and I didn't know about this feature.
Are you familiar with the older Windows Server version called Drive Extender? If so it seems these are similar but Storage Spaces apparently has more features.
I ask because if you are familiar with Drive Extender then you may be able to answer your own question. How are these files stored on the multiple disks, and were you able to access them from outside of the Drive Extender environment?
If yes, then I would assume the same with Storage Spaces. In fact there is a FAQ in the link below, (at the end of the article, that tells more about this;
A couple more links for you, in case it is useful;
I note from the MSDN blog one FAQ about migrating from Drive Extender to Storage Spaces, ie;
Q) I use Windows Home Server with Drive Extender. Is there a tool to help me migrate data from the Drive Extender format to Storage Spaces?
No. You will need to create a pool on a Windows 8 PC with a fresh set of disks. Then, you can simply copy data over from your Drive Extender-based volumes to a space within your pool. The functionality delivered through Storage Spaces is more flexible and better integrated with NTFS, so it will generally be more reliable and useful.
That may or may not be significant. If Storage Spaces changes significantly when W8 goes retail you may have to create a new Storage Space and copy the data over.
Limited information from me I know, but I hope it helps.