A team at PennApps had a project [1] which used a DNS-override to take advantage of the fact that Siri defaults to Googling things when it doesn't have a native approach. They could then parse these requests and see if they could do something cool without before going ahead and just Googling it. The example they used in the demo was controlling a Phillips Hue light with Siri commands. I thought this was awesome, one of the better hackathon demos I've ever seen. There really should be an easier way to do this an spoofing Google DNS, which I'm not comfortable with even though I trust these guys.

1 - http://betterthansiri.com/