The German website Macerkopf.de claimed to have obtained information related to on-going changes in iOS aiming to improve battery lifespan for the iPhone 4S.
It seems that Apple is currently putting all its resources to reach this goal. We are not talking about solving a bug, but rather, optimizing iOS code and used resources and components to decrease power consumption as much as possible. It seems that all features are being reviewed: Siri usage, GPS and phone-specific usage.
In the first major update of iOS (most likely 5.1), the main feature will be the improvement of Siri, as in most non-English language, it remains close to a beta version. Later on, Apple will keep developing Siri to make some functions and their activation fully voice-controlled (such as photo or video capture, switching on and off options, etc.)
Siri seems to be the priority for iOS development, and this is not surprising as Apple is working on associated services, as on the hardware level, competitors are closing the gap and now functions and features are the key factors to make the difference.