There is no permanent solution to this bug at this point in time. There are workarounds, but none that directly address whatever bad code created this problem. I'm leaving it to Apple to provide the permanently solution.
A Summary of the situation from my experience and reading:
1) There are TWO affected folders:
2) The permissions for both of this folders are DAMAGED on affected volumes. Repairing them does NOT solve the problem.
3) The terminal commands to make /Users AND /Users/Shared visible are only temporary. The folders disappear again with the next reboot.
4) I've watched an UNaffected volume decide to become AFFECTED with a reboot, having no idea why.
5) The 'Find My Mac' fix, including the reboot, has NOT worked for me at all. Kirk McElhearn found it did work, so huh?
6) I still have no comprehension why anyone brought iTunes 11.2 into the situation unless it was part of the cause. It doesn't apparently have anything to do with the solution that I can find.
7) There is a set of chmod commands, used to change the affected folder's permissions, that is reported to fix the problem. The method is fairly complex, well beyond an newbie or granny user's capabilities or comprehension. You can read about this workaround under David Helms' comment at Kirk McElhearn's blog article:
8) There is an AppleScript workaround that I do NOT recommend as it involves inputting your admin password, a VERY bad idea.
HEY APPLE: Your turn! Fix this ASAP please. This is seriously annoying.