It's a bit odd the way it works, but here is the solution:http://forums.mate-desktop.org/viewtopic.php?f=2&t=813http://chrisjean.com/2009/11/03/move-gn ... in-ubuntu/
Right-click the panel you wish to move and select “Properties”.
Uncheck the “Expand” option under the “General” tab.
Grab one of the edges of the panel by clicking on the left or right end (top or bottom end for vertical panels).
Drag the bar to the desired screen and position.
Check the “Expand” option in the “Panel Properties” window and click “Close”.
As a side note, the window list seems to automatically know what windows are on what monitor now!