Lord, you just can’t make this up. I had a call this week from the office person at a local non-profit. As is often the case in a small operation, she is one of two people with full administrative rights on the office G4 Imac.
She was trying to figure out how to change the name that appears in the “From” field in Microsoft Entourage. She had already changed the name in the Mac Address Book, which for better or worse is invariably integrated into every other Mac application.
When that didn’t work she figured that maybe what she should do is change the user name that was associated with her Mac log in. So that instead of “Administrator” the log in now read “Jane.” All in all a pretty good guess.
She went to System Preferences on the Mac, and chose Accounts. See the panel below?

That’s what you see on the Mac. Name, Short Name, and the option to Change Password.
Where you see “Chuck” she typed in “Jane”. She left the password the same and clicked the little lock icon and closed everything out. There’s no way to change the Short Name.
Everything looked just fine. She logged out and back in using her new User Name “Jane” and her usual unchanged password. Nothing changed so she figured that maybe she would change the name of here User Folder, the one with her docs and settings. So she went into Finder , found that folder and changed the name of that from “Administrator” to “Jane” too.
When she next logged in all of her desktop and all of her documents had disappeared. Gone, finished. Nowhere to be seen. All of her settings, bookmarks, everything. Gone!
She quite sensibly panicked.
I’ll skip the considerable web research, and tell you what we found.
If you change the name in your User Folder, that change doesn’t show up anywhere else. When you next log in, even though you have the same User Name and password, the Mac goes brain dead, can’t find your data, and instead creates a new User folder with the old name.
So all of your settings and data disappear. You can see the folder that used to hold them (In this case called Administrator), but now it’s empty. You can also see the User Folder with the new name (Jane), but there’s no way that you can log in to use it.
I think we fixed this by changing User Folder Administrator‘s name to OLDAdministrator, and User Folder Jane back to Administrator. Everything came back after another log in.
The secret is that the unchangeable box for Short Name, above, is really showing you the name of your User Directory.