Estimate the challenge percentage

Since September 25th (October 2nd in China) around 10 million people have been playing Mists of Pandaria. They have been leveling up their characters to 90, played new pandaren and/or monk characters, explored new zones, did daily quests, did pet battles, harvested vegetables, ran dungeons, did raids, fought in PvP, collected crafting materials, crafted, and did a host of other activities. All together they played over 1 billion hours of World of Warcraft: Mists of Pandaria. And I have a questi

World of Warkraft...