In case you, just like me, want to have a heavily customised keyboard layout configuration, possibly with different layouts on different input devices (I recommend inputplug to make that work), you probably don’t want your desktop environment to mess with your settings or, worse, re-set them to some default from time to time. Unfortunately, that’s exactly what gnome-settings-daemon does by default in GNOME and Unity. While I could modify inputplug to detect that and undo the changes immediately, it turned out this behaviour can be disabled with an underdocumented option:
gsettings set org.gnome.settings-daemon.plugins.keyboard active false
Thanks to Sebastien Bacher for helping me with this two years ago.