The reason PCI Express has not been released yet is because graphics card companies have been working on AGPx8 based GPU's for a long time (AGPx8 is still fairly new), as the GeForce 6800 is AGP.
Expect to see an AGPx8 ATI card for this generation - although ATI have been talking about PCI Express a lot more; hence the "ATI and PCI Express" text you see all over their site.
Only time will tell.