My last flight to LAX (from EWR) on a Friday evening had about 6 people upgraded after we had settled down in coach. On the return red-eye my wife had the same situation and was upgraded to a BF seat after having sat down in coach. Each time we had checked in on Co.com about six hours ahead of departure. The GA at EWR wanted to make sure everyone at the gate had boarded 15 mins prior to departure, and then processed upgrades while we were inside the aircraft.

Last minute availability seems to be the situation of upgrade inventory these days.