I run several multi-user machines and am having several issues with user management and security relating to LightDM in 11.10, specifically:
1) Shutdown is not working from either the Desktop or the greeter screen if another user is logged in (I would have expected a password/confirm screen);
2) After several "switch user" operations, LightDM will sometimes fail and deliver a black screen wih a flashing curser;
3) Possibly most concerning from a security point of view, users are able to access other logged-in user's desktop directly and without a password by using Ctrl+Alt switching between X-server instances (first logged-in user is on Ctrl+Alt+F7, second on Ctrl+Alt+F8, etc).
It does not appear that these issues are receiving attention so I'm wondering if anyone has used an alternative (such as GDM or LXDM) that is more functional and secure and whether there are instructions for installing.