While backlight control works fine for 2nd and 1st generation MacBooks, first of all 3rd generation MacBooks are not correctly detected because of 10-macbook-backlight.fdi. There is the line:
<match key="system.hardware.product" string_outof="MacBook1,1;MacBook2,1">
I've changed that to include MacBook3,1 and now it detects the MacBook correctly. But gnome-power-manager can't handle the backlight control because of missing interfaces. See the attached gpm.log for details.
Created attachment 17551 [details]