At TSMC
Nvidia is getting close to tape out its 28nm graphics core. The company is aiming to have a new chip in 28nm ready for autumn launch. The target time frame is Q4 2011 for the desktop chip and a bit later for the mobile one.
The chips are made by Nvidia's long term partner, TSMC, so there are no surprises there. TSMC is already taping out some 28nm network chips but graphics chips are far more complex and have billions of transistors these days. It might take them a bit more to get ready for billion(s) transistors graphics cards.
AMD (ATI) graphics is also making its 28nm chips at TSMC and unfortunately for them, Nvidia always gets more love. The specification wars are no on, as both companies have thermal limitations to heed, and as you all know, it is very important to end up at least slightly faster.
The real fight is scheduled for Q4 2011, asuming that both companies can execute flawlessly.