EA said:On a more pleasant note, Battlefield 2 hit somewhat of a milestone last night with over 52,000 simultaneous players. This is the highest number of players we’ve seen at one time for Battlefield 2 and almost 4 times more than the peak number of Battlefield 1942.
If it was 50'000 people playing at a time and each player played for 2hrs each that'd be 600'000 players a day. Bear in mind that not everyone who buys the game will play it every day and that's still a lot of people playing online, just not all at the same time.