Here's another story (more relevant to ID checking)...

A couple years ago while in the old BOS PC I scored a companion upgrade BOS-IAH (can you believe that... a BOS flight and on a 735!!) and by some error the PC assigned BOTH seats to my friend. So we had two boarding passes with his name on both (we were not aware of this) and when I got to TSA and my ID didn't match the guy said that, so my friend and I switched boarding passes (again, assuming we each had the other's, not aware of the same name on both). After switching, TSA guy looks at my ID and boarding pass again and lets us through. Only the gate agent noticed the double name upon boarding.