Well, mostly. The A.V. Club has put together a writeup on WoW's abandoned spaces -- and despite the day to day MMO crowds, there are a lot of them. Have you visited Shattrath lately? What about Dalaran? These old content hubs are now abandoned by players, only inhabited by NPCs and the occasional alt-leveler. In fact, there are plenty of zones in the game where you can find you're the only person there -- and when you aren't crowded in by people, you can take a moment to enjoy the solitude and all the game details you might miss if you were racing a druid to the nearest ore node.
It's feigned solitude -- the game's other players are just a zone or a whisper away -- but it still works for a change of pace. For more of this quiet musing, just head out to one of WoW's abandoned spaces yourself -- or read through the full article on the A.V. Club.