The video below demonstrates how Siri can be hacked to control your thermostat, but with a little massaging the hack could be used to make Siri perform a wide array of new functions. Let the games begin!
In the video, the developer @plamoni shows how he gave Siri the ability to control an internet connected thermostat. The hack sends his voice commands to a proxy server, which in turn enables Siri to get a remote readout of the current temperature or to change your thermostat's climate settings. It's a pretty cool trick, but the point of the hack is to build a framework so that developers can experiment with extending Siri's functionality far beyond what Apple has officially sanctioned. In theory, Siri could be used to control nearly any internet-connected device.
Unfortunately, the new hack won't allow any old schlub to get in there and start rewiring Siri. @plamoni has published the code for his proxy server on GitHub, but unless you've got some pretty sophisticated developer chops, it's not going to do you any good yet. The developer says he's thinking about adding some functionality which would make it easier to use his hack. Even if we're not quite in a place where we can make Siri bend to our will, remember that Siri hasn't even been out in the world for two months yet. It's not hard to imagine a future in which Siri's brain is more widely accessible for a host of new functions outside the Apple-programmed lot. Take that walled garden.