300,000 is the number of players it took to take down Blizzard’s Diablo III servers over the past weekend. 300,000 concurrent players, that is.
The open beta was a wild success then as far as stress testing goes, though not so much for actual players, seeing as problems of being unable to play the game due to connection woes were reported widely.
Funny, that, seeing as it’s a single-player game. It’s also the future, though.