You've got to love the big airlines.
We've got a trip to the UK planned shortly, and I don't know why but I decided to check the trip details today. Both the schedules had changed going to and from England, but the outbound trip was the most interesting. When I originally booked the flights, we had a 2 hour layover in Atlanta. With the changed schedule, the flight from Atlanta now leaves 28 minutes before the flight from Salt Lake gets in. And Delta, bless their hearts, hadn't re-booked us on an earlier flight. In other words if I hadn't checked, we'd only have found this out when we went to check in at the airport. All fixed now :)