I've personally run both Nvidia's Surround (GTX 280 SLI) and ATI's eyefinity (single & dual HD 5850s). The latter is definitely less of a hassle in my opinion. Its also usually lot cheaper as you can run it with two/three monitors or even with just a single card.
Here is a great post from tzetsin at hardwarecanucks regarding Surround and Eyefinity.
I absolutely without a doubt hands down suggest ATI's eyefinity. Anyone who argues this is an idiot and i'll tell you why...
First off, the biggest reason i recommend eyefinity to surround is that you only need ONE GPU. People are going to argue that with a resolution that large, SLI would kick its ass. They arnt wrong, but they're stupid. In REAL WORLD experience, i notice NO difference at all gaming on my dual gtx 480 vs my single AMD 6970 or 5870. so while technically the frames are higher on the SLI system, there is zero value.
Even if you were to notice a "slight" difference (and you likely wont) there are many other reasons against Surround. These include the extra cost of having a PSU that can power them, The fact that only SLI capable motherboards are surround compatible (higher cost as well as forces you into larger cases) Fermi doesnt run cool I dont care what anyone says, so you'll have to pay special attention to case cooling. I "had" to water cool mine, it wasnt a performance or asthetic choice. And if all that wasnt enough to sway you against it, if you didnt know already, Surround is still not "officially" supported by NVIDIA. Surround works ONLY on a couple of drivers that are getting pretty long in the tooth. Eyefinity is officially supported and is getting pretty mature actually.
Some people might say that eyefinity isnt any better because it needs a dongle, well that dongle doesnt require any special hardware, its 40 bucks and requires no extra power... not much of an argment. SLI is still going to cost you more than the cost of the extra gpu.
There is only ONE advantage to surround over eyefinity and that is you can have a "second" monitor active (3 in surround = 1) where you'd need a second card (not xfired) to run anymore monitors than the 3 grouped. Even that one advantage is moot considering that a slave junk card is however cheep you want, doesnt require any real hardware change and barely costs more power... and who has room for more than 3 monitors on their desk anyway?
Now IF you want surround AND 3d, you HAVE to go surround. but think long and hard before you decide, 3d will halve your FPS, so your going to have to run a 480 or better to enjoy anything even close to full IQ, its going to be RETARDED hot, you'll need extreme cooling, and/or headphones so you dont go def from the fans, if that doesnt deture you and you can invest the time and cash to make it work, surround 3d is pretty F*in awsome.