Friday night, two passengers suddenly showed up on the F seatmap just prior to departure (all upgrades had already been cleared, and we went out with two empty F seats). A couple boarded; it turns out that they had been VDB'd from
BE on IAH-STL to F on IAH-MSP and Y on MSP-STL the next morning on DL, plus hotel and meal vouchers and $700 ETCs each. Now that's a pretty nice deal.
I hope that UA pushed the ticket over to DL properly...