I'm using 2 monitors with Ubuntu 11.04 and can't for the life of me figure out how to move the Unity Dash/Taskbar/whatever to where I want it (the far left side of the left monitor). No matter what I do it remains on the left side of the right hand monitor. Has anyone else figured out a way to achieve this?
This can be set by adding the line to xorg.conf. Take attention to select desired monitor's section.
Section "Monitor" ... Option "Primary" "true" EndSection
I can confirm this worked for me with ATI Radeon card + manufacturer's driver: Catalyst 11.9 (Ubuntu 11.04). Maybe also applicable under different configs.