After Apple released OS X 10.9.3 yesterday, some users started experiencing a bug that hid their /Users folder. It appears that Apple has released a small iTunes update, numbered 11.2.1, to combat the bug. MacRumors forum member IzzyJG99 notes:
An update just popped up for me. iTunes 11.2.1 in the App Store. When it was done installing it had a little pop up about iPhoto Library. Now the User folder is showing up again.
Users can update to iTunes 11.2.1 via the updates tab in the Mac App Store or through OS X’s „Software Update“ drop-down menu.