Many users updating to OS 10.9.3 are reporting that their /Users folder is set to be hidden, not unlike how the ~/Library folder is hidden by default. However, this behavior is not happening to everyone, including me (but I have only updated one machine).
Perhaps needless to say: installing AppleScripts into any of the appropriate folders in the Users directory will be somewhat impeded by this phenomenon.
Bug or feature characterizations aside, if your Users folder is hidden after installing OS X 10.9.3, several people are suggesting resetting the "hidden" flag of the folder; but this flag is evidently re-set back to hidden on a restart of the machine. A relatively more thorough fix is suggested on the French MacBidouille forum and is also listed in the comments of Chris Breen's Unhiding the Users folder article at MacWorld. This fix has you reset PRAM, repair permissions, and then reset permissions on the Users folder.
Among other workarounds: From the Finder's "Go" menu click "Go to Folder..." and type in "/Users". Once open, drag the folder icon in the title bar to the "Favorites" section in the window's sidebar. The folder will continue to be hidden in the Finder but can now be accessed from the sidebar.
UPDATE: According to The Mac Observer this issue is related to having Find My Mac enabled and the iTunes 11.2 update and not specifically the OS X 10.9.3 update.
UPDATE ALSO: Apple fixed the issue in the iTunes 11.2.1 release on May 17.