Oh yes! This is a big shout out to Federico who's co-ordinating the work to make the multihead situation rock a little bit harder on Linux/GNOME.

Firstly, I'll point to the wiki page about the effort and now I'll say how I've got to a stage that's on the way to me not having to boot into a Less Free OS^TM in order to do presentations with an external projector.

My laptop has an nVidia chipset in and I'm using the Nouveau drivers (which are in Factory). I did have to do a bit of manual editing of xorg.conf. Specifically, I had to edit the Device section that relates to the display and the relevant section within the Screen section and I'll mention the latter first. My default colour depth is 24bit, so here are the lines in question (my changes are in bold):

  SubSection "Display"
    Depth      24
    Modes      "1280x800" "1280x768" "1024x768" "1280x600" "1024x600" "800x600" "768x576" "640x480" 
    Virtual 2304 800
  EndSubSection

The numbers are based on the fact that the built-in laptop display is 1280x800 and I want my external resolution to be 1024x768. The maximum width therefore is 2304 and maximum height is 800. Now to the device:

Section "Device"
  BoardName    "Quadro NVS 110M/GeForce Go 7300"
  BusID        "1:0:0"
  Driver       "nouveau"
  Identifier   "Device[0]"
  VendorName   "NVidia"
  Option       "Randr12" "true"
EndSection

Save the file, logout and log back in again.

Now, open the GNOME Control Centre and select Screen Resolution and you'll get the window that you can see below. Don't worry about the slightly ropey interface - it's a work in progress. What you see is the result of me having dragged the Iiyama monitor to the right of the AUO display rather than being a part of it - how easy is that?

I think a good aim would be to avoid having to edit xorg.conf at all and for this window to popup when an external monitor is connected but as the product of only a short amount of time's work, I'm really impressed. Nice on Federico, I'm in awe!

One last link: This is the tracker bug for multiscreen-related issues.