Hardware.info points to a presentation slide from NVIDIA showing the range of products the company's graphics chips power. The tagline reads,"From Super Phones to Super Computers". The site also noted a strange looking Mac notebook in the middle of the lineup.
The lower part of the body has a tapered rather than squared off shape like the original MacBook Air. Meanwhile, the screen has the black border of the MacBook Pro line. The MacBook Airs have all had silver borders on their screens ever since their release. NVIDIA also doesn't power any of Apple's Mac laptops at the moment, but is rumored to be powering the next generation MacBook Pros.
Still, we wouldn't read too much into the photo. NVIDIA did power the 2008 MacBook Air which did carry a similar look to the bottom shell with the tapered edges. Our best guess is that the photo is of the 2008 MacBook Air that has been manipulated to include the darkened screen border.
We frequently see ads and slides that seem to depict an upcoming device, though it's rare that they ever amount to anything more than creative artist renditions.
Update: As a number of commenters have noted, NVIDIA has been using this slide for quite some time and the desktop wallpaper on the machine is from Mac OS X Leopard.