It is expected that Music playback, iMessaging, Calendar managing, Reminders, Weather, Maps integration, E-mailing, Notes, Contacts searching, Safari integration, Wolfram-Alpha searching, and more are all available through Siri on the iPad. Here is a mocked up screenshot of Siri on the iPad.
Siri was ported to iPads back in October after the release of the iPhone 4S, but not through official means obviously. One tweak made use of a jailbroken iPad to get the voice assistant to work on the bigger screen. Do you think you will use Siri on the iPad?