This is more of a note-to-self. I had a problem in my recent upgrade to the latest Ubuntu in that my two monitors, when set to ‘twinview’ meant that the panels and task bars, and maximized windows spanned both monitors. What you really want is for these to be able to be moved from one monitor to the other, but when you maximize them they stay maximized in only one monitor.
The solution that I guessed might work, and it turned out did, was to comment out the ‘metamodes’ option in the Screen section of my xorg.conf. I.e.:
Option "TwinView" "1"
Option "TwinViewXineramaInfoOrder" "CRT-0"
#Option "metamodes" "CRT-0: 1280x1024 +0+0, CRT-1: 1280x1024 +1280+0"
That sorted out the problem as soon as I logged back in again.