This is a big deal, especially for any mobile ad networks, game networks or any app which relies on the UDID to identify users. Many apps and mobile ad networks, for instance, uses the UDID or a hashed version to keep track of who their users are and what actions they have taken. App publishers are now supposed to create their own unique identifiers to keep track of users going forward, which means they may have to throw all of their historical user data out the window and start from scratch.
Deprecated in iOS 5.0
An alphanumeric string unique to each device based on various hardware details. (read-only) (Deprecated in iOS 5.0. Instead, create a unique identifier specific to your app.)
If Apple does permanently phase out UDID access it could cause major problems for developers and third party services. One mobile industry CEO told TechCrunch that it would be an "extremely lopsided change" giving a Game Center and iAds another advantage over their competitors.
[Image via 9to5Mac]