Apple switched from NVIDIA to AMD for their current 2011 MacBook's, but it is rumored they'll be switching back to the green team for the 2012 MacBook's claims sources for SemiAccurate. In the last few years Apple have relied on a mix of AMD and integrated Intel graphics in their systems.
Apple are reportedly switching back to NVIDIA after a failed attempt on the most recent MacBook Air with an AMD Llano processor, which gave issues because of AMD's supply capacity. Apple is said to make the change next spring with Macs based on Intel's Ivy Bridge platform.
Of course, we take it with a pinch of salt, but then again, we know Apple like to change things up sometimes. If Apple is peeved with AMD, their only alternative for serious GPU power is NVIDIA. Next year should prove interesting times for Apple. Next-gen iPads, a switch back to NVIDIA for GPUs, iPhone 5, and we'll see how Tim Cook as CEO goes over a longer period.