This code has been updated and expanded - take a look at Web Speech Recognition on my web tutorial site Web Apprentice.
This demo was based on the tutorial Voice Driven Web Apps: Introduction to the Web Speech API by Glen Shires.
This is a minimal example of the API to help get you started. See Google's Demo for a more complete example.
The API captures segments of speech, sends them to Google for processing and handles the returned text.
A more complex example that also captures user audio and displays a spectrogram is HERE
NOTE as of 2013-03-08 the demo only works in Google Chrome
NOTE that this demo will not work if you open the page as a file - it must be hosted on a server.
View the source of this page to see the script. Change the language code in the source to suit your language (currently 'en-GB').
The reference documentation for the Web Speech API is HERE.
This demo was created by Robert Jones of Craic Computing and is freely distributed under the terms of the MIT license.