Blizzard Entertainment announced earlier this week that World of Warcraft has reached over 8 million subscribers worldwide. World of Warcraft boasts 2 million players in North America, over 1.5 million players in Europe, and more than 3.5 million players in China. For reference, Blizzard defines a subscribers as "individuals who have paid a subscription fee or have an active prepaid card...as well as those who have purchased the game and are within their free month of access."
With the release of The Burning Crusade expansion in the U.S. and Europe in four days time (January 16th), Blizzard expects to gain even more subscribers. The expansion will increase the level cap to 70, add two new races, a new profession, hundreds of new items and enemies, and much more.