Google Chrome 11 added support for HTML speech input API. " With this API, developers can give web apps the ability to transcribe your voice to text.
When a web page uses this feature, you simply click on an icon and then speak into your computer's microphone. The recorded audio is sent to speech servers for transcription, after which the text is typed out for you."
Google Translate is the first Google service that uses this feature. If you use Google Chrome 11 Beta, Google Chrome 12 Dev/Canary or a recent Chromium build and visit Google Translate (Click Here), you can click the voice input icon.
Right now, this feature only works for English, so you need to select "English" from the list of input languages.