This is not a real thing. Don't go crazy. The apparent version of Siri on the Android Market is, of course, no such thing, with the app simply re-branding existing Android voice functions and adding a Siri logo to Google phones.
It's actually quite a good advert for the things Google already does. The "Siri" app is literally nothing more than a shortcut to Google's voice actions feature, which has been letting Android users bark simple commands at their mobiles, like asking it to navigate a route, play music or send someone a text message, for a couple of years.
And as all it's doing here is placing a generic icon called "Siri" on the Android home screen, it looks like it's a perfectly legal thing for developer "Official App" to do. Morally a bit dubious, mind. [Android Market via TNW]