An estimated 1.2 billion apps were downloaded in the last 7 days of 2011

"In a new report, Flurry Analytics estimates that in the final seven days of 2011, 1.2 billion apps were downloaded worldwide across both Android and iOS, representing a 60 percent jump over a typical week.
More important, it is the first time the globe has punched through the billion-download mark, according to the technology company, which builds tools that thousands of developers use to track usage of their mobile applications."
Source:  Estimates from Flurry Analytics, reported by All Things D, 2nd January 2012