The Inq figured out the biggest thing in the die of ATI's Radeon X1800 (R520) is the memory controller.
ATI on the other hand had a different plan. It wanted to redesign the chip and it spent a lot of time to redesign its memory controller. It takes a big chunk of the die, but you can look at it as a long term investment. ATI will re-use this controller at least for the next generation as it can support GDDR4 and can address at least 1024MB of memory so it's here to stay.
This big memory controller paid off in OpenGL games and you can see that X1800XT will beat Geforce 7800 GTX 256MB memory in the games that were traditionally Nvidia only. And we learned that this new memory controller is far from being optimised so there is possible a fair bit more to come on that side.
The R580 which will be launched in Q1 2006 will use the same memory controller.
More details over at The Inquirer.