When the world is being torn asunder, isn't it best to remain inside? During a presentation at the ongoing BlizzCon 2010 in Anaheim, California, Blizzard president Mike Morhaime confirmed that the upcoming World of Warcraft expansion, Cataclysm, would be offered in downloadable format right on time and on launch day. When the game's December 7 release date was first announced, it wasn't clear if the digitally distributed version would lag behind retail copies.
It doesn't get clearer than this: You'll be able to purchase and download World of Warcraft: Cataclysm from Blizzard's site (which will accomodate pre-orders soon) at midnight, Pacific Standard Time, on December 7th. That means you can safely start questing, never having left the comforting confines of your home and risked contact with those crude human beings.