Most of my long-haul flying is done on dirt cheap fares, but I once got upgraded from coach to business on both legs of a CDG/JFK flight when I was FP Red:
- on the way out, by the check-in agent when he saw my preassigned bulkhead seat had been reassigned to somebody else, presumably travelling with a baby (in this case, I'm pretty sure the upgrade hadn't been preprocessed, but the flight was overbooked in economy and I had arrived very early at check-in),
- on the way back, by the lounge staff -- again, the flight was heavily overbooked in economy.

I was also upgraded from Tempo Challenege to Business at the gate once when travelling on a mixed class ticket (out in Tempo Challenge, back in Business) on an intra-European flight. It was the only time I was handed a new boarding pass at the gate. Even the agent looked surprised