Yay for old threads.
Going from low elevation to high elevation does nothing to the dissociation curve. What happens is that since the partial pressure of O2 is lower at higher elevation, a person occupies a lower pO2 point on the curve (which hasn't changed), which indicates a lower level of O2 saturation. Later, there are acute and chronic effects due to oxygen deprivation that causes a shift to the RIGHT. This is adaptive so that in the new equilibrium, such as in animals acclimated to the high altitude, the oxygenated Hb saturation is lower than at sea level, but the drop in pressure in the tissues results in a greater amount of O2 dumped.
Remember it's not the actual % saturation that matters, but the change in % saturation across a pressure difference. A shift to the right, especially when working in the cooperativity range, results in a larger % sat difference. A shift to the left implies increased Hb affinity for O2 at all pressures, which is a nono because it means O2 doesn't leave Hb when it's supposed to and tissues starve.