Agreed. I worked on PPC on the Xbox 360, and rarely had to worry about the underlying ISA, although when you did have to worry about it, things got pretty hairy

Agreed. I worked on PPC on the Xbox 360, and rarely had to worry about the underlying ISA, although when you did have to worry about it, things got pretty hairy and ugly, fast (think: DMA, cache coherence and other low-level stuff all ganging up to ruin your day). You also had to worry about the ISA when you were doing something performance intensive (that's when you start taking advantage of multimedia instructions and so forth; ideally you have abstractions for this, but they'll only take you so far).