I have same question like the user in 2008. Sorry for picking up this old threat, but:
when I create a ftp-user i can set the path under options.
normaly (in my case) this is for example:
will this ftp-user be able to upload files for other websites in client16`s account when I set the path to /var/www/clients/client16/ ??
can this user upload files for web42 and web43 ... than?