The Guardian documents it:
Batty writes that it took Twitter four years to see its first 10 billion Tweets but just the past five months to see the next 10 billion.
Read Write Web is a little underwhelmed:
It would be nice to know what percentage of those Tweets were sent by humans, and what percentage by robots, RSS feeds, Tweeting houseplants in need of watering and marketing sleazebags who re-Tweet reputable blogs' feeds automatically to give credence and cover to their occasionally original in-stream advertisements.
The tweet itself was a little incomprehensible, if not eerily instructive of the entire medium:
"So that means the barrage might come back later all at once."
Words for the ages.