I believe that the respawn rate for mobs is too fast. In quests like "lvl30 Battle for Hillsbrad [Elite]" the mods respawn so fast that no real progress can be made, even for 5 man groups.
I also noticed that in many other quests like the one on the rooftops of thousant needles, the Tauren there, respawn too fast.
In general, in caves or buildings, the respawns suround and overwhelm the players.
Even though it is nice for named mobs to respawn fast so many ppl progress the quests, I believe it is better to sacrifice a bit wait time for the satisfaction of completing a hard quest or many other quests.