The rivalry between previous allies Apple and Google took an interesting step with Apple's release of the iPhone 4s. The announcement of the hardware and new version of iOS was not the difference, Siri was.
While Apple portrayed Siri as a personal assistant on the phone who could set reminders and make calls, Siri is also able to search the Web on a voice request. In fact, Apple's Siri page does not even mention search.
This is Apple's first step into mass search, and while it may use Google's search engine (along with Wolfram Alpha), it will remove the users view of Google's ads. A direct strike at the jugular for Google.