As an addition to this question:
What remaining device fingerprinting privacy/security vulnerabilities still exist as of iOS 8? Can 3rd-party apps still access a list of other running apps? How effective is it to test custom URL schemes to determine what other apps are installed?
For example, there is some indication that the Whisper app is bypassing Apple's latest protections: http://www.zdziarski.com/blog/?p=4056