I just learned this today and thought there would be other VoiceThread users who would appreciate knowing.
If you are a Mac user who also uses VoiceThread, you should be aware that the most recent version of Google Chrome (23.0.1271.64) has disabled the ability to record audio with with flash based applications (like VoiceThread). If you've noticed your voice or webcam comment sounding robotic or not working at all, this is likely the culprit. Switch to Firefox or Safari until the issue is resolved. There is no known issue with recording into flash when using Chrome on a PC that I'm aware of.