I am leveling a Worgen on Stormrage server and I am experiencing terrible lag. 3-4 second delays every time I loot a mob/quest item or interact with an NPC.
I do not have this problem on Dalaran server. Mobs are looted instantly and there is no delay, so it is clearly a server problem with Blizzard.
It does hit everyone. I was getting it bad myself yesterday on Proudmoore server. Especially in Tiragarde. As you can see by that Mega thread it is a longtime ongoing issue. I suspect it has something to do with sharding or perhaps war mode.
Ion Hazzikostas has acknowledged the issue on one of his YouTubes.