One of the benefits of a Raspberry Pi is the amount of CPU power available for the money, and ths can be harnessed for all sorts of uses - including voice recignition. Ben Finio has demonstrated a useful project based on this technology with his voice-controlled power points. Doing so is easy - by hacking the remote from a set of wireless outlets the Raspberry Pi can easily control them safely without any mains wiring.
Then it's a matter of configuring the Voice Command software which is available as part of the PiAUISuite (Pi Alternative User Interface Suite) by Steven Hickson. This sends voice captured by a microphone on a connected USB camera to Google for recognition, whose results are then used by the software to control the wireless remote. Check out the following video for a demonstration:
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