"Confirmed" upgrades on United used to work. Back in the day, if a cabin was mostly open, I could apply one of my confirmed upgrades and voila. Upgrade confirmed. I don't think I've seen a confirmed upgrade actually upgrade one of my flights in quite some time. I was especially surprised for an upcoming SFO-JFK-SFO trip. Take a look at how empty both business class cabins are. I'm still on the waitlist for the upgrade, unfortunately.
On the second flight, there are only two seats taken in business class, according to the seat map. This map is basically empty, and it still won't confirm. Does anyone else have better luck?
Of course, United does not allow complimentary premiere upgrades to be used on P.S. flights so the upgrade isn't "worthless," as I wouldn't even be in the running for an upgrade if the instrument didn't exist.