A multi-GPU HD 7950 CrossFire setup is certainly not a cheap thing to get. With $900 for the two graphics cards alone you could get a large TV screen, a console and a couple of games for it. We see good performance scaling in most titles of our test suite, except for Batman Arkham City and Elder Scrolls Skyrim. Battlefield 3 at 2560x1600 also fell back to single GPU performance, even though lower resolutions scale just fine. We noticed the same problems in our HD 7970 CrossFire review with an earlier driver, so it looks like things are not going as fast as they should with AMD's driver development.
With this generation of cards AMD introduced their new ZeroCore power saving technology which really can shine in CrossFire. In a CrossFire setup only a single card will be active when not gaming; the other cards will be essentially switched off, consuming only 1W of power and producing no heat or noise. Once a gaming session starts, the additional card(s) will instantly wake up and be ready to provide their full power without any manual switching or software configuration required. It seems AMD has found the holy grail for multi-GPU power consumption reduction.
Other options for high-end multi-GPU gaming are currently the GTX 590, which comes at $750, but offers less performance. A dual card GTX 580 setup will be more expensive, at similar performance compared to 2x HD 7950. Two Radeon HD 7970 cards certainly provide more performance (about +13% at 2560x1600 in our testing), but with $1100 this configuration is much more expensive than the $900 of the two HD 7950s that we tested today. So it looks like the dual GPU HD 7950 CrossFire sits in a nice niche for the time being.