Upgrading to OS X 10.9.3 e iTunes 11.2 that Apple released recently, brought us a somewhat strange side effectie the user directory where the "Home" folder resides disappears after reboot as long as Find My Mac is enabled. Still do not worry that your files are safe and sound, but a little more "hidden" although luckily it is a minor problem with an easy solution.
Actually the update to OS X 10.9.3 does not influence this bug, but it is the iTunes 11.2 installation the one that seems to create this curious disappearance in the users folder.
However, if you need to see files you just have to go to the finder and in the sidebar there will be a direct access to your files in your user folder.
On the other hand, the user directory is where the Home folders for each user in your session. You can display your own Home directory in the sidebar of Finder windows which gives you quick direct access to your own files. But if you really need to see the entire user directory, this is what we should do:
Launch Terminal within Applications> Utilities, once open we write the following
sudo chflags nohidden / Users
With this we will make it not hidden and everything will be as before. It seems that this move by Apple more than a mistake is a move to bring OS X closer to the iOS file system, which means less control over the files and this process of hiding the Users directory seems part of this transition.
Soon we have the official opening of WWDC 2014 with the most likely presentation of OS X 10.10 and it will be where we can check with the first betas if this is really the path that Apple intends to follow.