They have a lot of world phase like the goblin starting area and the quest phases otherwise are more liberal than in WOTLK where at hand in the quest would change the world and everyone would fade and the npc would glitch. The phasing for this are more liberal, it seems the hubs are more static and the surroundings are phased which is nice for a lot of characters in one place.

I am sort of used to going through zones and pushing everyone forward and clustering, I am not seeing any extra problems traveling via flying mount going from place to place. Flying to lich king is if anything easier, maybe its the high populations right now or something. Usually that is one of the worst journeys for me.