Great to see many positive experiences rather than problems. A few years ago I was flying to HNL once a month on UA. Always used upgrade certificates that could be bought. One evening the flight was full, so I didn't buy upgrade certificates. Once on though, it was clear that several of the 1st class passengers didn't show. Waited until the door was about to close and then asked if I could upgrade. The agent said sure and asked for my certificates. Told her I needed to buy them. She looked at the purser who said that the flight was going and then smiled and said OK move up. Hadn't planned it this way and would have been happy to pay. Later, another passenger asked to move up who had been on the wait list and was denied. When he pointed at me and complained, the comment was, "You weren't fast enough!"