Often I use a USB microphone for quick Voice Overs (for timing) and when I'm on the road I tend to just hook up my Zoom H4N to the laptop and record comments and VO's using it directly into FCP or Quicktime 7.
If you hold down Option while clicking on the volume adjustment menubar item you'll see this:
Instead of the normal volume slider. This is a quick way to access these common settings and get to the the Sound Preferences.
Hitting Option + Volume Up or Down will also take you directly to the Sound panel in Settings.