Anandtech spill the beans on everything they know about R520 and friends, everything they can tell us, at least.
The part that everyone wants to hear about is, of course, the Radeon X1800 based on ATI's long awaited R520 GPU. Due for introduction later this quarter, the 90nm R520 will be a 16-pipe, 16-shader processor design with a number of different SKUs based on the GPU. Internal ATI documentation specifically claims that the R520 series will ship at launch, just as NVIDIA's 7800GTX and 7800GT series shipped and launched on the same dates.
[Anandtech]