In Apple's iTunes Connect, under Manage Your Tax Information, there is this question:
Do you have any U.S. Business Activities?
In general, you have U.S. Business Activities if you have employees in the United States, or own, lease or control equipment or other assets in the United States that you use to derive revenue from the iPhone Developer Program.
Should I tick
No in response to this question?
I don't think I have any US business activities: My business is registered in Europe. My license for iOS Developer Program was sold to me by Apple Ireland.
... except for this:
My web site is hosted by a US hosting provider in California, including a web service that's part of the app's functionality. Email is handled by Gmail. Support ticket tracking is hosted with a company in New York.
My revenue comes from app sales. There is no paid subscription or other source of revenue apart from the app sales.