It was only three months ago that Facebook announced that it had reached 200 million users worldwide. Today, CEO Mark Zuckerberg says the social network has passed 250 million active users. And back in January it was just 150 million.

Facebook has been accused of under-counting users in the past. According to comScore, Facebook had 316 million unique visitors worldwide in May, but not all of them necessarily had accounts.

No matter which way you slice it, adding 50 million users in three months is nothing short of amazing. Most Websites would kill for a fraction of that growth. How long before Facebook reaches one billion, and can it beat Twitter to that milestone?

Update: Here is a heat map, showing the global distribution of Facebook’s growth over time:

http://www.facebook.com/v/234513010483