Why not a default guest user for public files ?
Example : an accademic structure work on file internaly and then decide than everybody can see/download a file and some infos.
Of course it"s possible to create a guest user for this but it will be more convenient to just allow/disalow guest browsing to /docMgr /collections /files without a login box
By default user are considered "guest" (if this option is allowed) unless they login.
I am not sure but D-spaces and Cern Invenio have similar feature.