I've been following this technology for some time (~8 years now) and I can tell you DrEvil is right. back then, using a 1Ghz AMD CPU I could barely put more than 50 objects on the screen. the primitives were the only thing you could use (spheres,cubes,etc.) if you wanted to get any sane performance. Even now, download and play warmonger without a PPU and see if your state of the art machine can pull it off all the way through - and we are talking about novodex here, one of the best and fastest SDK around for a while now.
Consider this: when 3dfx started most of the 3d was on the CPU and it was said that no one needs GPUs to do more than send graphics at high resolutions (remember CGA?) to the screen.. the CPU will do all the rest. 3dfx proved them wrong and other followed suit. I think PPUs will go through the same path.