This is such an astute acquisition by Apple and what you're going to see is that most of the news organizations will not cover it beyond "Apple bought some search company".
The technology behind Siri is actually mind boggling. Apple has been investing in developing Semantic tools (which is really the next frontier) and Siri is yet another big leap towards taking computers closer to artificial intelligence.
For instance they have spoken about Latent Semantic Mapping
being added to some tools and lo and behold they have an employee well versed in the technology. Jerome Bellegarda
Google acquired Aardvark
for its social searching tools but I think Siri is on another level with regard to their ambitions hence it's rumored Apple spent upwards of 200 million dollars for Siri (who say they've invested 200 million dollars in their R&D).
The money is here. Siri works with roughly 40 external structured API (like Yelp, Google Maps, OpenTable etc) there's really no limit to how many API services they can support. They then run these API through their "secret sauce" which according to one of the slides is what they call their Domain & Task Models and then on to the UI which is their "Guided Dialog"
Is this a threat to Google? Yup. If Apple creates the "mashup of all mashups" that delivers excellent results then people will flock to the service and Apple will reap huge licensing rewards on the backend and won't even have to advertise (though that could be another revenue stream).
I don't think you can look at it any other way. This acquisition is larger than what most are assuming.