It looks like it is raining Siri hacks courtesy the SiriProxy created by Pete Lamonica.
Developer Ian McDowell has created multiple custom plugins to use Google Voice and control Mac apps using Siri.
As you can see in the video below, Ian McDowell demos sending a text message using Google Voice rather than the native messaging app.
He then demos another custom plugin to wake up his computer.
The third custom plugin will allow you to control iTunes playback on a Mac using commands such as Open iTunes, play or pause a song, play the next song or previous song, increase or decrease the volume, mute/unmute etc.
The final custom plugin will allow you to open or close any apps on a Mac and also minimize windows.
All of this has been possible thanks to SiriProxy created by Pete Lamonica that allows developers like Ian McDowell to create custom plugins that can intercept voice commands and perform any action that is programmable, scriptable etc.
[via YouTube, Thanks Tim for the tip!]