ATI is working hard on R600. It won't finish it until the end of the year but it aims to make the fastest chip to date. We heard that the chip might achieve and even surpass the magical 1000MHz clock.
The fastest that Nvidia and ATI can do with 90 nanometres is around 650 to 700MHz and we know that you won't be able to overclock much more with a 90 nanometre chip. This may mean that R600 will be a 65 nanometre component.
We expect that Nvidia might introduce its G80 a few months before ATI, we expect G80 at late summer or early autumn, while we know that R600 wont see the face of the earth until late Q4. Things can always get delayed, as you know. ยต