I agree it's a big "IF". IF Siri works as advertised, then it really could be revolutionary. I remember being pumped up by Google's demo of voice recognition, only to try it out and find it novel and cool but not dependable and accurate enough to use in all my real-life situations. And it's difficult to correct errors, or clarify requests in a conversation manner like Siri.

Another reason to hope is that Siri had 19 people when Apple acquired it and most of them are still at Apple. I would imagine that Apple scaled their team significantly. Who knows? Maybe 100 engineers working on it, since it's a cornerstone of the next generation of mobile devices (and probably coming to desktop in the near future too). But Google doesn't seem to have the same priority on natural language processing as Apple does cause more than 50% of Apple's revenue comes from the iPhone. How many engineers at Google are working on voice recognition and natural language processing? Maybe somebody here will know. Maybe max 10 engineers?

Apple also will be forced to scale Siri across multiple languages very quickly, especially if it works well. Currently they have English, French and German. But tons of people will want it, so that motivates Apple to innovate even more.

I guess we'll see very soon how good Siri on the iPhone 4s really is.