I'm working on a site that will have multiple users. Each user should only be allowed to see the folders that they need to see. How do I control the visibility of folders based on users? I only see how to do it based on roles.

Local roles save the day again: - create a 'FolderViewer' role. At the root level give it the permissions to view the folder. Probably 'View' and 'List contents' or something. Do not give it to your users on a global level (in the acl_users folder.) - in each folder, use local roles to give the 'FolderViewer' role to those users who should see it. You'll probably want to disable the folder viewing permisisons for whatever role your users usually are. Probably 'Anonymous' (or 'Authenticated' in 2.4) in a default install. This is very similar to what you might do with multiple 'Owners', but more flexible (and without letting them change things.) --jcc (local roles are fun)