Permanently set monitor as primary

By opening System Settings > Displays you can change your "primary" screen by dragging the black little bar to the display you want and hit the Apply button. Restarted my PC and i didn't have to use xrandr anymore ^_^

Better explanation than mine you can find here: http://www.thebinaryidiot.com/archives/2011/11/11/gnome-shell-3-2-and-multiple-monitors/

What I did:

places>home folder. Under view, check show hidden files. find monitors.xml and open it with text editor. make a copy just to be safe.

identify the monitor you want to be primary (vendor brand, resolution etc) and look for the command line < primary>no< /primary>. change it to < primary>yes< /primary>

Save the doc and reboot to see if it took.

hope that helps someone out there.

echo -e "xrandr --output DFP2 --primary" >> ~/.bashrc

Or add xrandr --output DFP2 --primary at the end of .bashrc