With the release of OS X Mountain Lion, Apple added loads of new features into the operating system. This feature is called Siri Dictation. Siri Dictation allows you to use you voice to type text into any text field, you can talk to your computer to write tweets, emails, status updates and school work.[youtube http://www.youtube.com/watch?v=aE_u8CDCkbc&feature=plcp]
It is a really great feature but unfortunately requires and internet connection.