Chrome 21 was recently released, but I have not seen any working examples of getUserMedia for recording audio.
I've seen some nice examples for working with the webcam, but none that are able to record audio in a format that you could upload to a server:
http://neave.com/webcam/html5/
WebRTC is saying that recording in this way may not be possible yet, even with the Chrome update: http://www.webrtc.org/faq-recent-topics
I have had success using Flash to do this and save as an MP3, WAV, or OGG file. I've also found ways to do it in Java. I think doing it natively in the Browser would be amazing.