The9, which is the company that runs Blizzard's World of Warcraft in China, has announced today that the game has hit a full million concurrent players (which means that they've had one million people playing the game all at the same time) following the release of the Burning Crusade expansion there last year. Here in North America, concurrent users hasn't really ever been as high (although that is of course unofficial data, and we don't have information after the first month of this year). But MMOs are a different beast in China and other Asian countries -- not only do players pay-to-play (instead of a monthly fee, many players often pay hourly or daily, which means concurrent users equals paying users), and there are actually three games that have hit a million concurrent users over there (while here, WoW is far and above the largest MMO online).
Still, it's quite an achievement. It's interesting that it's coming so late in the product's life -- it seems that, just as over here, the expansion had a significant impact on player interest. Definitely a big milestone for Blizzard's game in China.