Stashed in: Square, @lizgannes, @evelynrusli
According to Evelyn Rusli's NYT Dealbook article on Square: http://dealbook.nytimes.com/2012/04/18/square-said-to-seek-250-million-investment/
Some previous Twitter stats I've stashed.
Note in particular Liz Gannes' excellent article on 4 tiers of Twitter users, which cited 100mm active users and 230mm tweets/day as of September 2011.
Black Widow | Dustin Curtis
Facebook, Twitter and Pinterest ‘Drive As Much In Store Purchasing As Online Purchasing'
Tumblr Went Toe to Toe With Twitter During VMAs, Per Data Firm | Adweek
What user numbers make for a "hit"?