15 billion apps have been downloaded from the iTunes app store

"Apple® today announced that over 15 billion apps have been downloaded from its revolutionary App Store™ by the more than 200 million iPhone®, iPad® and iPod touch® users worldwide. The App Store offers more than 425,000 apps and developers have created an incredible array of over 100,000 native iPad apps.
“In just three years, the revolutionary App Store has grown to become the most exciting and successful software marketplace the world has ever seen,” said Philip Schiller, Apple’s senior vice president of Worldwide Product Marketing. “Thank you to all of our amazing developers who have filled it with over 425,000 of the coolest apps and to our over 200 million iOS users for surpassing 15 billion downloads.”"

Source:  Press release from Apple, 7th July 2011