ZD Net speculates Apple may dump ATI because of their acquisition by AMD.
Apple's aging PowerMac G4 ships with NVIDIA graphics (GeForce 6600, 7800 GT or Quadro FX 4500) but the graphics chip supplier for the new "Mac Pro" desktop is rumored to switch to back ATI. The Mac Pro, which could be announced as soon as 07 August at WWDC, is rumored to ship with ATI Radeon X1600 Pro and X1800 Pro graphics.
Will Intel allow Apple to continue to working with ATI on graphics after the company becomes wholly owned by rival AMD? I think that we'll probably see Intel gently "suggest" that Apple switch to another vendor for graphics technology in 2007. Once the dust settles I bet that all Macs from here on out will ship with graphics from either Intel or NVIDIA.