This is incredibly useful! The existing paradigm, that users can make a "decision" about whether or not to use an app based on the permissions it requests, is just not true. We shouldn't have to make the decision not to use Angry Birds or Pandora simply because they request location information, or information about the "phone state" (er, unique ID).
This feature finally allows us to continue using the apps we want, without having to give them access to all of our personal information in exchange.