I'm running Ubuntu 10.04 and i'm an 'mid-advanced' user, so my terminology may not be correct here.
System records (captures?) sound from the external microphone normally (checked with arecord). However, when I start any 'heavier' app (like firefox) it stops recording (arecord hangs). This is especially annoying while skyping as I can't do anything during the talk and sometimes the capturing stops even without any action during skyping (suddenly the person stops hearing me).
In case if this happenes I close skype (otherwise it hangs upon the next step), type "sudo alsa force-reload" and the capturing (recording?) works again until the same thing happens.
In the meantime I've reinstalled the system and the thing still occurs.
edit: The problem still occurs after upgrade to 12.04.1