I've read "Unix_Groups" and "Security" pages on the wiki to know how to make any user's home directory inaccessible by other users on the same account.
There seem to be very complex solutions... Some via crono jobs too.
I've instead simply run this in every user's home dir:
chmod g-rx ~/
It seem that in this way the problem is solved. Isn't it?
Am I missing something? ^o)