Following on from the region panel, we now have an updated “Screen” panel for the control-center. Richard worked on the initial version (which you can see in older revisions of the control-center for GNOME 3), and I finished hooking it up this week.
Not much to say about this, except that the lock screen timeout preference now changes the underlying preferences for both “on AC” and “on battery”, as well as the idle time (which is used by a number of desktop components like your IM application).
I'm also very glad that we managed to get rid of the brightness levels based on whether on battery or mains power. This usually worked exactly as you didn't want it to. Now, just use your keyboard shortcuts for those instead of hoping to gouge somebody's eyes out every time you changed power source.
See also the design page for more information about the changes made.