Michael,

It's hard to make definitive statements about perceptual rendering, because this is really where profiling tools differentiate themselves -- each one has it's own secret sauce.

Generally, there's some weighting -- it isn't just a linear desaturation -- and in-gamut colors typically get less desaturation than out-of-gamut ones.

The effect is usually quite subtle because our eyes tend to judge relative color, rather than absolute, and because if you're making the judgements on the monitor, what you're looking at is pretty close to sRGB anyway.

I'm trying to find out what happened to part II of sharpening -- it was here, but it seems to have dropped off the list on my author's page. I've sent the appropriate inquiries to teh appropriate powers...