As long as the aspect ratio is set correctly, Ogre runs fine with eyefinity. When the usual extended desktop mode for multiple monitors is enabled, Ogre sees each monitor as a separate display device. When eyefinity is on, Ogre only sees a single display device.
Here's Ogre running with a simple scene. I played with the viewport settings (dimensions of 0,0,1.5,1) to fake the effect of 3 monitors without having the third, so the current right hand screen is really acting as the middle one.
The problem with eyefinity though is that standard rendering using a projection matrix just doesn't work that well at extreme wide angles. You get distortions on the edges like this:
As long as you look at the centre monitor and use the sides for peripheral vision, it's not too bad. This is how all current games will run with eyefinity.
I prefer a more dedicated solution though. Here's Ogre using one camera per monitor with the side cameras facing away. With monitors positioned so they curve around you a bit, it gives undistorted views to either side (if you had 3 monitors).
That's a bit exaggerated though, effectively 288x90 degree view. It would look much better in games to simulate the real field of view of the monitors as if they were windows.
Another issue: bezels. Eyefinity currently has no bezel control, which would hide pixels behind the bezels to make the scene more realistic. But with my multiple camera method in ogre, I've got it working fine.
Oh, and now I REALLY wish Ogre had a DX11 renderer, the demo of what Hull and Domain shaders can do is amazing (better quality than parallax occlusion or cone step mapping with none of the flaws, but as fast as bare normal mapping).
