Starbucks has processed more than 42 million mobile payments in the US

"A novel new way to pay by iPhone or Android at Starbucks locations is proving too convenient for caffeine-crazed customers to pass up.
Starbucks has processed more than 42 million mobile payments since the U.S. launch of its mobile pay program less than 15 months ago, the coffee company shared exclusively with VentureBeat.
Starbucks released “mobile pay,” a prominent feature of the company’s iPhone and Android applications, in January 2011. Customers use the mobile app to load money on to a digital Starbucks Card and then present a 2D barcode to pay at the register. Baristas simply scan the barcode using the scanners they already have at their cash registers. Mobile pay first launched in the U.S., but has since migrated to Canada and the U.K., and Starbucks recently made it available to customers ordering from drive-thru windows.
In December 2011, Starbucks revealed that it had processed 26 million mobile payments. Adoption continues to grow expotentially, the company said."

Source:  VentureBeat, 9th April 2012