I learned Friday that you need to keep checking EVEN if when you board it looks like there are no empty seats up front. I got a battlefield upgrade after boarding on Friday under such a circumstance. When I had boarded first class showed full and all had checked in. But someone must have had a late connection or missed the flight (security at EWR was horrible Friday) and an open seat opened up and I got it. I had stopped checking my pda thinking that I was out of luck, but I won't do that again, even if first class looks to be full and all checked in at boarding time.