Also, W3i is not recommending developers collect MAC addresses instead of UDIDs. W3i is recommending that developers collect users' MAC addresses and associated UDID. With two "primary" keys for each user, developers do not lose their old tracking data when Apple prevents apps from reading UDID.
http://techcrunch.com/2011/10/28/w3i-suggests-ios-developers...
Also, W3i is not recommending developers collect MAC addresses instead of UDIDs. W3i is recommending that developers collect users' MAC addresses and associated UDID. With two "primary" keys for each user, developers do not lose their old tracking data when Apple prevents apps from reading UDID.