I'm interested in unique information that is beyond typical user knowledge or control.
As of iOS 7, users can easily protect local physical tracking by controlling radios (cell, WiFi, Bluetooth) in Control Center. There are also now explicit privacy controls for Location Services, Contacts, Calendars, Reminders, Photos, Bluetooth Sharing, Microphone, and Motion Activity, that require user consent for each app to access.
I'm particularly interested in the information an app (and its controlling server) can collect behind the scenes. IP address is an obvious one. Vendor ID and Advertiser ID are also out there, but there are ways to change those. Can apps access the device name or any other unique device identifiers (e.g., device phone number, MAC addresses)? Can non-updated apps still access deprecated identifiers such as UDID?
Without cookies, how are app makers and their integrated 3rd-party trackers fingerprinting users and devices? Especially concerning are technologies that allow others to track your activity across apps from different makers.