Wall Street Journal reports that a new study from Beijing data-analysis firm Cnzz.com predicts that China will hold more than half of the global market for online gaming by 2012. Given the current 20% growth rate, the online gaming market is predicted to reach 41 billion yuan ($6 billion USD). They currently report 338 million web users among their population, with two-thirds of those users defining themselves as online game players.
Of course, the main branch of online games in this case are MMOs. In October, six of the ten most popular games in China were MMOs, with four of those being subscription based models. World of Warcraft holds the top spot in that list with "the most registered players and peak simultaneous online users." (The recent bickering between WoW and NetEase may make that a temporary position, however.)
The full story from WSJ blogs contains more details, and is a good overall read.