During its WWDC presentation, Apple announced that it has 575 million iTunes accounts. This is a 6x increase since late 2009 and the number of accounts is growing at about 500,000/day or 44% compounded annually.
Examining iTunes revenue (gross), Dediu points out that revenue per account has dropped about about 50% since 2009 but that seems reasonable considering the 6x increase in accounts.
"In absolute terms the graph shows that an iTunes account generates about $3.2/month in transactions. Put another way, during the last year, an average of $40/yr of economic value is generated by every iTunes account."
If you consider it unlikely that a customer has an iTunes account without an Apple device, then Dediu calculates that three years ago an Apple customer spent $400/yr on Apple products but now spends $300/yr.
The report also looked at the Enterprise Value (Market cap minus cash) per iTunes account which showed that from 2009 until late 2012, Apple's users were valued by the stock market as likely to create a net present value of about $1200 in earnings. Currently, that has dropped to $440 in earnings. ie. That means that a current Apple customer is now expected to buy just 1.8 iPhones ever.
Although the rate of spending of each customer is decreasing, the number of new customers is increasing more rapidly. As this is happening the company’s equity is being priced such that an Apple user is considered less than half as valuable as she used to be—from 3.2x revenues to 1.5x revenues. This change in user value has been quite abrupt, happening only within the last nine months. What could justify a drop in user value would be a drop in customer satisfaction or loyalty. So far, I have seen no evidence of this happening.
Take a look at the charts below or hit the link for more details.