I do use a single user to access a couple domains and this isn't the best situation either. I want to protect two domains from one another, and protect various paths within a single domain from different users. But because I've created the whole site under a single user I'm having a problem getting permissions to do what I want.
Ironically I've found that SFTP allows a user access to see the entire server, and anything created in the user's group, and we can't change that. Where FTP does allow a user to get locked to a single path and related subdirectories. To me, that's stupid.
Maybe we can learn something from one another?