Comment 49 for bug 742544

Andrea is right. The option exists already in oneiric's Gnome 3 display settings panel. It's just not obvious to all users because the bar is small. But you can drag it between monitors.

And certainly Andrea is right that at least up to Unity 4.16, this worked in changing the screen on which the launcher appears. Apparently it doesn't work since 4.18 though (due to lp:unity r1609).

<design>
But there is one fundamental problem here, even if the Unity behaviour of honouring the primary monitor is to be restored by some config option, to resolve this bug. The problem is the bar icon you drag around in the Gnome 3 display settings is horizontal because it's designed to represent the Gnome 3 shell panel. If we restore its ability to control Unity too, then it really should be drawn as a vertical bar as well, to represent the Unity launcher.
</design>