I have been to the USO on the A Concourse in DEN and it's a welcome place to hang out before a flight (or between flights). It is small but the volunteers are the friendliest people ever. The snacks are decent but I don't go there for the snacks. They have a place for families with kids, a computer area, comfortable lounge chairs to watch tv and a sleeping area (same lounge chair but in a darkened room). The list to volunteer there is so long, it would take you 3 years before a position becomes available.