If you're interrested into this, you shoul reaéd about the Gelato rendering engine. it is a 3dsmax/maya plugin developped by nvidia, that uses the GPU to accelerate rendering of photo-realistic scenes. It works with quadro cards but also with geforce since FX 5200.
It's real nice, but pretty useless to the average person. I don't know how they're going to run x86 programs on a GPU, but thats why I'm not designing the program.
for the average user, the point is not to run a complete app on the GPU, but to offload the CPU from heavy floating point computations... juste like they already do for 3D graphics.there would be some "GPU-accelerated" operations inside the programs
what my sick and twisted mind was thinking is this:
rig up some software that allows you to fill all the slots with grapic cards.
how much gflops can you pull from 3 GX2s and a couple PCI cards.