I found MAC randomization in iPhone 5s (details below), but not in iPhone 5 and iPad Mini. I suspect that this has to do with the OS architectural difference between old and new generations of iPhones.
In iPhone 5s, MAC randomization happens only under the following conditions:
- Phone is in sleep mode (display off, not being used)
- Wi-Fi should be ON but not associated
- Location services should be OFF in privacy settings
I'm looking forward to the findings on iPhone 6 and 6 Plus. It looks like Apple has implemented this appropriately. I have no issues with my MAC address being shared when I actually connect, but not before.