Amazon has more than 215 million active customer accounts

"“Amazon has more than 215 million active customer accounts,” Tom Taylor, Vice President, Amazon Payments says in a release today. “Login and Pay with Amazon enables companies to make millions of our customers their customers by inviting online shoppers with Amazon credentials to access their account information safely and securely with a single login.”"
Source:  TechCrunch, 8th October 2013
Note - The iTunes app store has 575m