Setting some user permission groups? Allow editing on only password protected accounts?
Yes. Just like Windows Access Control Lists, but a lot less complicated. Individual users and or groups would work.
What I see is the following:
At startup of a client (that is connected to a library server) the user is prompted for a username and password. Choose Username from a list, and enter password with a on-screen keyboard. If you have read on all Music, Video and Images you can see Views for them all, but if you don't have access the View is not visible. Users with write restrictions to specific parts of the Library could also be set. You can't access the tag system, or you'd get a restriction prompt if you try to edit things you don't have the rights to. Whether or not the play count and similar should be updated I'm not sure about. Adding playlists from the client should be available anyway I think, as well as views, and would follow the user if he changes client. A guest account with no password and no write privileges could also be used.
The minimum should be to be able to set read only or read and write for the whole library per user. It could also be client based, but you'd miss many good opportunities like roaming play lists if you simplify it that much.
A system like this would be easiest and most elegant if it's locked to theater view, but could also be possible in standard view.
It would be very elegant for a digital home, but could be used in a lot of other scenarios I suppose. Like a media server system for Hotel rooms, and Music/Video at bars maybe? Basically anywhere that contains several user groups and you want to be able to delegate limited access to different groups to prevent library disasters, or that people play with unnecessary things or things not suited for the situation or person.