I was really surprised when I saw Delta sell upgrades on a flight from SFO to ATL last week. There were six seats left (DL has a screen that shows how full each cabin is). I wasn't on that flight, but it made me suspect that upgrades on DL must be a lot easier to get compared to CO--that has been my experience on DL to date. Having seats in FC to sell--well, I don't think I have seen that on a CO flight since the week after 9/11. (Or, when a flight heads off to Europe with empty seats, and elites sitting in coach on full fares willing to pay with miles--a different story! )