To remove a user, select a user in the main window by clicking on it, and click on Remove. After confirming the removal, you will be asked if you wish to remove the user's home directory and mail spool. You will normally answer Yes. After these files are deleted, you will be asked if you want to search the entire file system for files that have been ``orphaned'' by the removal of this user. Orphaned files are those that are not owned by any user in /etc/passwd. Since you have just removed a user from /etc/passwd any file that user owned will now be orphaned (except the home directory and mail spool, if you deleted them). If you answer yes, the search will proceed in the background, and all files found will be chown-ed to nobody. To find these files, execute the following command:
find / \( -group nobody -o -user nobody \) -print