Blizzard Entertainment, Inc. announced today that subscribership for World of Warcraft®, its award-winning massively multiplayer online role-playing game (MMORPG), has continued to climb, recently passing 10 million worldwide. Interest in the game has remained high in all regions, with thousands of new and returning players signing up through the holiday season. World of Warcraft now hosts more than 2 million subscribers in Europe, more than 2.5 million in North America, and approximately 5.5 million in Asia.
Source: http://www.blizzard.co.uk/press/080122.shtml
I'm looking forward to seeing any MMO in the future beat these kinds of numbers, just incredible.