PCI Express 2.0: Scalable Interconnect Technology, TNG
 

Purchasing a PCI Express 2.0 graphics cards at this time is future proofing more than anything else; we haven't noticed any performance differences when comparing PCI-E 1.x chipsets to PCI-E 2.0 chipsets with the newer GPUs, and we don't expect you to either. PCI-E 2.0 may prove more useful as a way to provide four x8 slots that each offer the same bandwidth as the older 1.x x16 slots. With Triple-SLI, Tri-Fire, and talk of GPU physics accelerators, including additional high-bandwidth slots on motherboards makes sense.

http://www.anandtech.com/cpuchipsets...spx?i=3192&p=1

Another one by Kristopher "FCG" Boughton for Anand, another interesting read.

Why can't we ditch the southbridge? That would make motherboards layouts less complicated.

Ditching the southbridge means you just ditched all of your SATA ports, sound, and everything else that uses I/O like USB ports, PS/2 ports, etc.

I guess you hadn't looked to closely at some of the Nehalem platforms though... some of them ditched the northbridge ;)