growth has slowed (at points, reversed entirely) since the release of The Burning Crusade, today it's finally hit 9 million active subscribers world-wide. The game reached 8 million subscribers in January, hit 7 million last September, and had 6 million last March. For those of you not trying to do the math at home, these numbers tell us that they averaged 160k new active subscriptions a month from 8 million to 9 million, 250k new active subscriptions a month from 7 million to 8 million, and 330k new active subscriptions from 6 million to 7 million. Though with a new expansion coming (I imagine we'll be getting plenty of news about it at this year's BlizzCon), I can only imagine we'll see another subscription bump -- and perhaps actually see the predicted 10 million subscriber year.
So grats to Blizzard for reaching another MMO milestone!