As I understand the process, the Windows 8 upgrade will copy your existing files and settings into \Windows.old, including:
- PerfLogs
- Program Files
- Program Files (x86)
- Users
- Windows
It will then create new folders for all of the above, and migrate the files into the new folders. The \Windows.oldfolder is really just there as a part of the upgrade process, but it does act as a temporary backup folder. If you don't need anything from there in the first month, then you're not likely to need anything from there ever (as most / all of it is already in the new folders, and the old folder is likely taking up gigabytes of space).
Now, if you've upgraded from Windows 7, then congrats, everything has been moved to the new folders, including installed programs and drivers.
If you've upgraded from Vista or earlier, then your documents and settings have been migrated, but you're expected to reinstall the programs yourself, and the upgrade makes this clear. If you're foolish enough to create shortcuts into*\Windows.old\Program Files* and hack the registry to point into that folder, then you've dug your own grave.
(I came here through a Reddit link, thought I'd copy my explanation over there to the original thread here.)