In my case, it was on a Mac on a PowerPC CPU. It's a far cry from the limited resources of early personal computers, but this was at a time when 3D was hitting big time - the Playstation had just come out - and I was trying to get performance and effects like a GPU could provide. A hobbyist could get decent rasterization effects from a home-grown 3D engine, but I was working as far forward as I could. All that unrolled code, careful memory access, fixed-point math... I spent a lot of time hand-tuning stuff. It wasn't until I dug into a book on PowerPC architecture that I found some instructions that could perform an approximation of the math quickly, and suddenly I was seeing these beautiful, real-time, true-color, texture-mapped, shaded, transparent triangles floating across the screen at 30fps.
It was about that time that the first 3DFX boards started coming out for Macs, though, and that was the end of that era.