I am another ATI Eyefinity user, I think you will find more and more triple screen users crop up with the release of the 5000 series ATI cards.
As mentioned it seems that in game by default with no modification the game is Hor+ (game properly extends the FOV across all screens without cropping)
The game also picks up my 5760x1200 resolution on its own without any modifications.
The problem is the game menu system and other 2d elements like the HUD, it just zooms to fit the width of all 3 screens by cropping the top and bottom so you can not see or even navigate the top 1/3 and bottom 1/3 of the menus.
It doesn't just make the game awkward to play, it makes it impossible since you can not see or select many elements within the game, cant even exit! Have to alt+tab (in the demo anyways)
Pictures are worth a thousand words and should make explaining this a lot easier.
Normal 1920x1200 Main Menu
http://lh3.ggpht.com/_nNcVLzdKf-c/Sz...2-22-14-57.jpg
Normal 1920x1200 In Game
http://lh3.ggpht.com/_nNcVLzdKf-c/Sz...2-22-29-59.jpg
Surround 5760x1200 Menu
http://lh5.ggpht.com/_nNcVLzdKf-c/Sz...2-23-12-21.jpg
You can see the zoom, doesnt break this part of the menu since it was a small one but...
Surround 5760x1200 Mission Select
http://lh4.ggpht.com/_nNcVLzdKf-c/Sz...2-23-19-19.jpg
Take something like the missing select screen and you see the problem start to form.
Surround 5760x1200 In Game
http://lh6.ggpht.com/_nNcVLzdKf-c/Sz...2-23-30-40.jpg
Get in game and now you see how great this game can be in surround, full Hor+ on all the 3d in game elements. But...
Surround 5760x1200 In Game Build Menu
http://lh5.ggpht.com/_nNcVLzdKf-c/Sz...2-23-38-07.jpg
Now you see the problem... Cant see the unit select part of the menu.
So looks like if you can find a way to scale down the 2D elements/menu's your game is all fixed and ready to be played at a higher level, surround gaming.
I have the demo right now, not getting the full game until I see this support added. Not meant to be taken as a threat just a truth because I only like to play games that support my surround setup.