I wanted to restrict other users' access to folders that existed prior to my upgrade to OS X, like the subfolders in my home folder.
Files and folders that were on the hard disk prior to upgrading to OS X are not assigned to a user or group. They take on ownership by whatever user is logged in. Using the Finder: Show Info to change the Privileges does not work. Any user logging in is listed as the owner with rw, r, r privledges. Group is usually "unknown."
To restrict access, you can log in as the user you want to own the files and copy them. Then delete the original. A faster method can be done via Terminal using "chown". You must sudo to use this command:
sudo chown [user shortname] filenameI did this to a folder and, voila, logging in as a different user I couldn't open the folder and got the "do not enter" folder icon.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20011130185023429