I had a call today from someone who had changed their home directory's name in OS X. This is a bad idea. The way permissions are set in OS X you can do this if you are an administrator. Users who have not been given administrator privileges lack the rights to make such a change. It reminds me that I saw a problem a short time ago where users can enter short user names that are longer than 8 characters. This causes problems for the unix underpinnings of the OS. These are things that should be fixed to prevent people having problems with their systems.
From what I've seen users should change the permissions on the /Users/ directory to prevent accidents. The command:
% sudo chmod g-w /Users/
will change it so that users with Admin privileges don't accidently change the name of their home directory. The % is not a part of the command but the end of the prompt where you type the command