[JOURNALIST WARNING!]
Just to let you know, while I post here usually as a pilot, in this case it is a local Denver story so I 'm wearing my editor hat today. But just reading for deep background information - nothing for publication, no specific questions to ask.
Our story has a quote from a denver aviation official to the effect that the Tv show "Mythbusters" has demonstrated that a gunshot to the airframe skin or a window will not EXPLOSIVELY decompress a pressurized plane:
http://en.wikipedia.org/wiki/MythBus..._Decompression
On another point, Denver Airport official said it must have happened "near Charlotte", since the plane "did not return to Denver".(Yeah, I know - I'm just quoting him!) But that ties in with the news report quoted previously here that it happened on final approach.
[update - our story for tomorrow says the incident occurred at 9:50 Denver time, 11:50 Charlotte time, and the flight was due to land (according to FlightAware) right about 11:50 - so final approach sounds correct (and a bad time to be distracted by loud noises!)]