Online Chinese Game BNB Records 700,000 Users
Thanks to simon for the heads up that casual online game BNB has a record of 700,000 concurrent users. The Chinese game is a casual online experience where families pit themselves against other families. For comparison the game Eve Online regularly has 10,000 concurrent users.
I think they're talking about single server (or single "universe") games. Everquest and DAOC and all them only host about 3,000 people on each server or "universe".
Most likely though, this game is not a concurant world, it's probably instanced it most cases, where the play areas are split off from the rest of the world much like Gunbound where there's basically different chat channels that you can join games in (which, once in game, you no longer exist on the server).
As a minor side note, Eve Online is the only US based game that runs a single server, single universe game (largest online population) which is probably why they picked that one (there's many lesser known korean games, japan, etc).