Privacy is a big big deal for me. It's why I detest Facebook and I have virtually stopped using it and why I am hoping Google+ will act as a good counterweight. So, when I read that Apple has removed the unique device identifier (UDID), I initially did not pay much attention to it until I realized that this could be a preemptive move to protect user privacy. At worse, give Apple an advantage over other networks and developer.
So, what is this UDID, what is used for, and why did Apple remove access to it? Privacy concerns, to gain an unfair advantage over others on the iOS devices, or both.
Think of UDID as something like your social security. As long as you're "you", well, it's unique to you. And beyond that, it allows others to keep track of you. On your mobile, it's how ad networks and developers keep track of you, what you do, and probably where you go. It's how they can target ads and services at you.
However, many apps transmit your device's UDID on the iPhone were done unsecuredly and unencrypted. It's probably worse on Android and other mobile platforms. By eliminating developer access to the iOS device's UDID, it provides a measure of privacy.
Now, Apple isn't outright getting rid of it. Developers are not left in the cold but rather this is a gradual thing. Instead, Apple wants developers to create ID specific to their own apps.
If anyone does like this, it'll be firms that use UDID to track users across multiple apps - like advertising or analytics companies.
For you or me, it's not going to change at all as far as how our iOS apps and iPhone will operate. There will be a level of privacy we did not know we didn't have but now will.
Obviously, there are likely ways around that. Advertising or social networks can bad together and use their own implementation. User data will still be collected in one form or another. But it just won't be as easy as before.
Now, if only Google would do the same...
Source: Techrunch, Appleinsider, TUAW has a very good explanation if you want more information.