The "New iPad" does not support Siri, the popular voice recognition and decision engine included with the iPhone 4S. Siri is known both for its ability to play music based on voice commands and the ability to scan the web and answer basic questions, like how many pizza resteraunts are in the nearby area or giving the weather forecast.
The 3rd generation iPad does support voice dictation, which may be the most important piece of Siri as far as the iPad is concerned. Voice dictation can be activated by tapping the microphone icon when the on-screen keyboard is being displayed. More tips on using the iPad's voice dictation.
Why Doesn't the New iPad Support Siri?
There is no official word from Apple on why Siri was not included with the new iPad, but the most popular speculations concern the iPad not being an "always connected" device like the iPhone (Siri requires an active Internet connection) and Apple wanting to create a unique iPad-Siri experience before releasing it on the tablet. Other speculations include a delayed release to ease the transition into the 4G network and wanting to keep Siri an iPhone 4S-only feature in order to drive more iPhone sales.