Why wait for PCI Express? I just saw the bandwidth numbers and they are very impressive but there is nothing that needs the bandwidth yet.
Video doesn't use 8X AGP yet (same throughput as AGP 4X). So video card bandwidth has to double before AGP 8X max's out.
Memory bandwidth is handled on the CPU with the Athlon 64 so no advantage here.
Optical drives are at their max read rates now,
HD are starting to push IDE especially with RAID stripping and SATA will but that not an issue unless you do video editing or graphics work.
Doesn't seem to be much incentive to trash all your IDE hardware investments until spring 2005 at least. Especially with Nvidia going the translator chip route and ATI probably going to have to follow to avoid the massive expense of maintaining 2 product lines.