Secondary qualities and self-location

There is a strong pull to the idea that there is some metaphysically interesting distinction between the fully real, objective, observer-independent qualities of things as they are in themselves, and the less-than-fully-real, subjective, observer-dependent qualities of things as they are for us. Call this (putative) distinction the primary/secondary quality distinction. The distinction between primary and secondary qualities is philosophically interesting because it is (a) often quite attractive to draw such a distinction, and (b) incredibly hard to spell it out in any kind of satisfying and sensible way. I attempt such a spelling-out after first trying to pin down in more detail what we want from the primary/secondary quality distinction, and saying a bit about why that is such a hard thing to get.