I have had about half a dozen op-ups on domestic QF in the two years I was SG, all on red e-deals and mostly between MEL & SYD. The nicest was when they rang me as I was arriving at MEL for my flight, saying it had been delayed and asking me to head to the service desk near the gate soonest. There a couple of agents were frantically trying to move people onto the earlier flight. "Y's full" I heard one of them say, and shortly thereafter I was given a boarding pass for J 
Being only SG at the time I was very happy with how proactive QF was with trying to look after passengers.
Another good one was when I was going to DRW. I'd ticketed:
MEL-ADL as a JASA
ADL-DRW as a JASA
DRW-ADL in cash Y
ADL-MEL as a JASA
Then DRW-ADL as a JASA was too expensive. But when checking in at DRW I was given a boarding pass for J, which was full. Thanks Qantas!
