I noticed while levelling yesterday that in the Kun-Lai Summit region of Pandaria, the Sha of Hatred was wandering around just north of the Eastery Rest.
It seemed to walk around in a large circle, very much like a pre-defined path for the several hours I was in the zone completing quests. In addition to seeing this big hulking monster, it seemed like the rare/champion enemies we ran into while levelling were scattered quite consistently over the landscape, resulting in us getting the 'Can we find more like that?' achievement for killing them all.
This lead me to thinking, are the rare spawns and world boss spawns pre-defined for specific parts of the world, or are they randomly generated, leaving all of my observations down to being the first through the zone with all the spawns up?