I had the task to record a short screencast. My plan was to do it on my MacBook as it has a decent performance (and no problems with the audio in the virtual world client as my Ubuntu laptop). On Windows I know the free and good software CamStudio. But for OS X I didn't know a solution, which could achieve that with free of charge software, so I tried to find one.
For the solution you will need two pieces:

• CamTwist
  
• Quicktime Broadcaster
  

CamTwist is able to stream your desktop (I used "Desktop+" to share a single application window only) and the Broadcaster is able to record the stream to disk. The recording of the audio stream is also supported! Some hints for setting it up:

• in the CamTwist preferences add the broadcaster to the list of "Only load the CamTwist driver in these application" in der "Video Apps" tab
  
• in the CamTwist preferences, "General" tab I changed the video size to a higher value to get a better screencast quality (remember to restart both: CamTwist and the Broadcaster!)
  
• in QuickTime Broadcaster select "CamTwist - CamTwist" as source and check the "record to disk" checkbox
  
• in QuickTime Broadcaster (in the "Details") I used the "Manual Unicast" as I didn't install a streaming server (like Darwin) which would be needed for "Automatic Unicast (Annouce)"
  
• in QuickTime Broadcaster press "Broadcast" to start the recording (the video location can be set in the preferences, default is the "Movies" directory)
  

If you have any questions just post a comment! I'll try to update this entry accordingly.