updated 01:19 pm EDT, Fri May 16, 2014
Terminal command may offer temporary fix
Yesterday's OS X 10.9.3 update contains a bug that is hiding the Users folder for some people, accounts say. The folder is essential in OS X, since it contains the home folder and personal files for each user account. Those files are still typically accessible through sidebar tabs, but the hiding of the folder itself may still cause problems.
A temporary solution involves running a Terminal command, "sudo chflags nohidden /Users". This is undone each time a Mac is restarted, but a simple AppleScript set to run at boot can launch the command automatically. Another alternative, once the Users folder is exposed, is to control-click on it and select Make Alias. The alias will provide quick access to the folder even once it's technically hidden again.