Well, what is there to say about Eyefinity? I mean, there's the obvious that it's pretty cool. It's also fairly easy to setup, you just need an active display port to dvi/vga/hdmi (assuming your monitor doesn't support DP natively). Besides that, Catalyst Control Center also makes it fairly easy, with just a few clicks and you've got Eyefinity with bezel compensation.
But what does it really add? Recently I saw a post calling for DICE/EA to ban people from using Eyefinity in Battlefield 3 - at least online. It was compared to wall hacks (to see people through walls) and aim bots (auto aim cheat). It should go without saying, though, that this line of thought is completely whack. Does it give an advantage? Maybe a little, sure. However, I find that for the most part, as far as the side screens go, I'm only really seeing about 20% of them. After that you get a lot of image stretching and it's tough to make anything out.
I think, ultimately, Eyefinity is really only good for immersion. I kind of want to compare it to PhysX. Yeah, it adds detail and can offer a "wow" factor, but it's not game changing and it's not available in every game. Not yet, anyway. Originally I had imagined that you'd have a really great field of view, but if you want to go past around 70-80, at least in BF3, you wind up with a lot of image stretching, aka "fisheye" effect.
How about some negatives? Well, for one, you need 3 monitors. Duh, right? But that's not cheap. Ideally, you'd buy three Samsung MD series monitors (MD = multi display) plus a triple monitor stand. We're talking $450 per monitor, plus a $200-300 stand. Samsung sells them altogether as a package for $1800, but you could probably do it for $1400 or so. Your other option is to go cheap, buy some low grade 1080p monitors like the S23A300B. Maybe having the monitors at a funny angle, and much too far below your eye level, is ok with you. Maybe you don't care to get a monitor stand. Fine, there's always that option. So what other issues are there?
Well, some games don't like eyefinity. I tried The Witcher 2 and it doesn't work. I spent some time googling it, and there isn't a whole lot of info. I did see a screenshot of it working, so there's that, but I never got it to work for myself. How about Dirt 3? Seems like racing games are a great candidate for it, right? Well, actually, it works out of the box with this one. For the most part you get the nice wide screen with a decent FOV and it definitely gives a good sense of speed when you get objects flying past your peripheral vision. There is one issue, though. Cockpit view. The one view I was most excited to use with Eyefinity. Basically, the FOV in that view gets completely messed up so the steering wheel looks like it's waaaay far away. Your whole car is squished inside a single monitor and then the side panels show basically just these stretched out doors. Took me a while but I did eventually find the solution to that. Just had to sign up to some forum to download a fix, which then automated the process of modifying the camera file of every single car in the game... right.
I also tried Metro 2033. While the large display size worked fine, it introduced it's own issue. In this case, it seems that mouse movement has some sort of correlation to screen size, and basically with the ultra wide screen you wind up with an uber sensitive horizontal movement, while vertical remains relatively normal. For many people they'd have to just suck it up and deal with it, but I'm lucky enough to have a programable mouse which allows me to adjust vertical and horizontal sensitivity. Even then, the mouse movement in the menus is excruciatingly slow.
So what's my final verdict on Eyefinity? I think it's not quite there. I think that games like Battlefield 3 are few and far between, and for all the console ports there's going to be even more troubleshooting for us PC users. I think Eyefinity is cool, and it can be worthwhile for some people. It does help really get you into the game, even if it's not making you some total bad ass because you can see sideways - honestly, by the time you notice a guy coming through the door 78 degrees to your right, you're already dead.
I would recommend that unless you have a lot of cash to burn and already have a really killer PC, Eyefinity is probably something to pass on. Yes, it is very cool... but me? I'm seriously looking at a 2560x1440 monitor. Or 3D. We'll see what happens.
Some screens I took: