Desvora of Doomhammer complains on the WoW forums that there are a lot of heavily camped quest mobs in the Outlands, and that it makes it really difficult to complete quests when you're running around with ten other people each trying to get the first tag on a named mob. She names a couple of mobs in Zangarmarsh, which has a TON of "kill the boss/chief/overlord of the wasps/bats/naga/ogres" quests, that she waited at least an hour for.
Drysc says that trying to be the first to tag a mob can "get the heart pounding", but Desvora just thinks it's a waste of time, and that respawn rates should be increased. I sort of agree with her -- having your group wait "in line" with five other groups from both factions can be pretty annoying, especially when everyone is consecrating/hellfiring/arcane explosioning to try and get the tag on the mob before it even fully fades into existence. I haven't had any really long waits, but as a melee player, I'm either left uselessly clicking the air and feeling dumb, or accidentally attacking an Alliance player and being turned into a grease spot.
Have you had serious trouble with any quest mobs?
(And yeah, spawn camping is mostly used to refer to players killing players at spawn points, but since people are tagging these mobs just as they spawn, I figure it's somewhat appropriate.