Apple using Radeons across the board for iMac and Mac Pro.
If you take a closer look at the Mac Pro and iMac refreshes this week, you'll notice that Apple has ditched Nvidia graphic parts in favor of strictly choosing ATI GPUs.
From a technology perspective, Nvidia right now has the shinier bullet point list with its Fermi-based chips, but all iMac and Mac Pro options are comprised of ATI's Evergreen family.
That's not to say that Apple has switched sides, as the company employs Nvidia chipsets and GPUs across the entire MacBook, starting with the GeForce 320M in the 13-inch MacBooks to the GeForce 330M discrete part in the MacBook Pros.
This could be a sign, however, that Apple and AMD are forming a stronger relationship. Earlier this year, rumors did the rounds that Apple may be considering using AMD CPUs in its upcoming computers.