my USB headset failed to be recognized, hear sound or use mic. I found this interesting article online http://openradar.appspot.com/11427549 about
AppleUSBAudio.kext lacks valid OSBundleCompatibleVersion key / 10.7.4 (11E53)
so I tried rolling back this kext to earlier 2.7.9 version and rebuilt cache repaired permissions etc. reboot. Went to sound prefs and BAMM! USB Headset is now recognized and working. This was on a Dell d630 Laptop running 10.7.4 Lion hope it helps someone.