Flew FRA-DEN yesterday through IAH. I was on the 9PM flight to DEN but landed at 6:30 so I went to the gate to see if I could switch to the earlier 7:45 flight. I had an expensive international ticket with a GPU applied. I arrived at the gate just after the agent had upgraded #1 on the list to the last first seat.
When she saw my reservation she realized that I would have gone ahead of that person so she downgraded him which caused me to go to the top of the list get the last first class seat.
I was just happy to get a seat on the earlier flight and never asked her to do this. I was blown away by her service.