iTunes 11.2 made the /Users folder disappear temporarily, if you're using iCloud's Find My Mac feature. Apple fixed it with an iTunes 11.2.1 update that appeared later in the day. And now the company has explained the change in a security post. Apple:
Upon each reboot, the permissions for the /Users and /Users/Shared directories would be set to world-writable, allowing modification of these directories. This issue was addressed with improved permission handling.
A file permissions exploit like that is a pretty big security hole. But Apple's first reaction was to make the /Users directory disappear all together, which caused understandable consternation for users. To be clear, the file permissions problem was fixed in 11.2.1. iTunes 11.2 apparently took a brute force approach. iTunes 11.2.1 instead actually fixed what was broken.
A strange about face for Apple, and a curious misstep. It's good that it was fixed, but I have to wonder how iTunes 11.2 was pushed out the door like that to begin with. Didn't Apple realize that making directories arbitrarily disappear was bound to cause concern?