I'd heard a lot about domestic US flights…

Americans strictly follow boarding groups, and military personnel and their families also board first (Houston/San Antonio — I couldn't verify this elsewhere). There's supposed to be an air marshal on board, which I can't confirm. Either way, sitting in the same row as a SEAL made me feel safe enough. Otherwise domestic US flights don't differ much from European ones — except that the aircraft operating them don't look new at all.