Zynga has 58m active daily users in 175 countries

"The company updated its stats, noting it has 230 million monthly active users, down from 232 million when it first file for an IPO in June. It has 58 million daily active users in 175 countries. Those users play 2 billion minutes a day and engage in 4 billion in-game user-to-user connections a day.
Zynga said that, according to AppData, its games are played by more daily active players than the next 14 social game developers combined. Zynga said it has four of the top five social games on Facebook, based on daily active users."

Source:  Data revealed by Zynga, and reported by VentureBeat, 4th November 2011