Theo Valich from Bright Side of News claims the first GT300 GPUs were taped out between January and March. However, it's unclear whether the A1 silicon is ready for mass production, a second tapeout may be necessary but the details are kinda vague.
Valich claims bot ATI and NVIDIA are having problems with TSMC's 40nm process, and that both companies are testing with the alternative company. He suggests that NVIDIA may opt to get it done on a 32nm process by GlobalFoundries if TSMC's 40nm process doesn't deliver good yields.
The site also received confirmation from multiple sources that the GT300 GPU, which is internally also referred to as NV70, will have 512 cores, a 512-bit memory controller and 256GB/s to 280GB/s of memory bandwidth. Furthermore, Bright Side of News also has a bit of information about the codenames of this next-generation GPU, which will likely be launched as the GeForce GTX 300 series. The GT300 is actually the codename of the Tesla version, while the G300 is the desktop GeForce card and there's also the G300L, this is an upcoming Quadro workstation card.
According to Valich, the first photos of GeForce GTX 300 graphics cards should be leaked to the web between now and Computex.