Although the iPhone 4 and newly released iPhone 4S have many similarities, the most significant new feature of the 4S is perhaps Siri.
Siri is a voice-recognition software that can aid in many tasks such as note-taking, scheduling, and information finding. Essentially, people can play with existing features on their iPhones using voice control through Siri. The sophisticated system is unlike other voice-control software because it is able to recognize and comprehend commands and questions at an advanced level (in other words, the system can recognize contextual/more subtle commands).
Much like how other Apple features have been adopted by other companies, the author believes that a feature similar to Siri will start appearing in other phones and technologies.
Technology as advanced as Siri is bound to make people feel apprehensive, and although some of the tasks that Siri can perform seem excessive, I predict that people will begin to use Siri for tasks that require efficiency and speed such as note-taking. However, until Siri is able to accommodate more people (through region or understanding accents), the popularity of this new feature will only grow gradually for now.