My Y->J upgrade on QF74 cleared no problems, and after getting on board, I see why.
F cabin was full. Downstairs J cabin had 2, count 'em, 2 PAX. It was a ghost town.
No idea about upper deck, but I noticed it was all X'd out on EF around 3 hours prior to boarding, so I would have thought it was empty up there too.
EF showed a full Y+ cabin (Y+ and 2 rows of J) and a full Y+ sold as Y cabin, as well as around 50% load down the back.
I can only imagine that freight was a large amount of this flight, as I have it from a good source that a large number of seats were marked as not for sale on this flight. Still, 72000 points from Y to a F seat was well worth it for a 14 hour flight IMHO.
All my flights currently booked, as per other peoples reports, are available to upgrade although I'm not going to bother for domestic.