When i using xinerama - dual head, the taskbar only display in secondary monitor(head/desktop). There aren't possibility to change moitor(head/desktop) to display taskbar.
I'm not sure, but I think it depends on how the Xinerama layout is set up in the X config file. I think if you change the layout that the second screen is 1px or above the other the taskbar will show up on that screen. Don't know much about Xinerama, though.
Absolutely, all you need to do is to change the Xinerama layout.
Ok, guess this won't be fixed in Xfce.