Let me start by saying that I realize that unity's screen locker is not the same thing as gnome-screensaver. That having been said, there are major regressions in functionality with the advent of Trusty. Virtually every site that uses Linux in any sort of public computing areas makes use (or used to, at least) of gnome-screensaver's "logout-delay" and "logout-enabled" functionality, which would, after the screen had been locked for a pre-determined amount of time, present a "Log Out" button that would end the user's session, optionally running a custom command to do so. This is vital, lest people walk away from their workstations, rendering them unusable by others until they are rebooted.
unity's lock screen mode provides no way to do this. Right up until the final beta, it was possible to swap out unity's lockscreen mode for gnome-screensaver, but that was removed as well. I wouldn't mind if it was possible to configure the alternate use of a screensaver, but Unity goes out of its way to ensure you can't do this. If there's some magic way to do this, by adding an applet to the panel when in lockscreen mode, or by invoking some D-Bus black magic, I'd be happy to hear about it.
But really, removing this level of functionality while simultaneously preventing any workarounds, is a real problem.
Steps to reproduce:
1) Log in to a unity session.
2) Lock the screen.
3) Observe that org.gnome.desktop.screensaver gsettings keys are not honored.
4) Examine the com.canonical.unity* schemas and observe there is no way to enable this behavior.
