hmm..
pci-e is "bigger, better, faster and stronger"

- is more expandable (current machines only use 16 lanes, or 2 8 lane distrobutions for CrossFire or SLi, while PCI-e can support up to 32 lanes, and 2 16 lane configurations (or 4 8 lane, or any other possibility)
- provides more bandwidth to the graphics card (interface bandwidth) which means demanding games like Doom 3 (which utilizes full AGP 8x (only game to ever do such) get a few % more performance on PCI-e over AGP, as their not hitting the ceiling of interface bandwidth