It's a voice search tool that seems to work a hell of a lot better than Siri.
Seriously, find a buddy with an iPhone or newer iPad and try it yourself. Do a search on Siri, and then install the Google app and try the same searches. I consistently get better results with Google.
Siri ends up doing a web search on anything but the most basic of questions, so you might as well just cut out the middle man and ask Google directly.