Dual monitors works fine, except that the settings suddenly change. This happens very often, sometimes several times in a few minutes. It is very irritating having to set the settings again each time. Suddenly mirroring is set to on, sometimes the monitor switch places (from left to right and so on), and most of the times the screen resolutions are also changed.
I use Gnome Shell. I have tried unity with the same result. I use an open driver. I have earlier used fglrx, with some better results (still happens, but not so often), but can't install it sucsessfully after upgrading to ubuntu 12.10.
I know there is a similar question about this issue, but it's not answered. I hope someone can help me.