The last time was just this year before COVID hit, when a Storm Ciara shut down down London Heathrow for 2 days. I 'volunteered' to postpone my flight without making a fuss, since I absolutely didn't mind extending my v̶a̶c̶a̶t̶i̶o̶n̶ business trip by a couple of days.
Though I was half expecting, half wishing for it, BA bumped me up to business class and that too on the upper deck. I like to think they did that because of the inconvenience they thought they subjected me to. It wasn't a window seat but I couldn't care less. There are only 5 rows of seats upstairs, so it really did feel like being in a private jet, with 2 attendants just for those 5 rows. Especially since the upper deck is a comfortable 2-2 configuration with an extra wide aisle, as opposed to the packed 2-4-2 configuration on the lower deck, even for business class. [1]
That was my last flight this year and I'm grateful that I could have been lucky enough to experience this before the 747s were retired; now I'm left wondering how flying again in economy would feel like having experienced this.
[1] https://www.seatguru.com/airlines/British_Airways/British_Ai...
The trip was LHR to JFK.
Pricing was ludicrous -- I think around AUD $600 (one way). This would have been 10% of list. The joys of ID90.
I have a handful of recollections. Most of the seats were empty. I could not stand fully upright in the aisle (I'm 188cm, or ~ 6'2"). Breakfast was delicious, and it was five courses. The whole flight was very noisy. At cruising altitude I was sure I was seeing curvature of the planet (I concede this may have been wishful thinking, or an artefact of the windows).
It was about four hours, and you really did land before you took off, on that particular leg.
At the time - young & holidaying - this wasn't as big a deal as it would have been in more recent years, when work obligations transformed travel from enchantingly wondrous, to onerous obligation.
Many people have reported this, and it's widely publicised so perhaps not so wishful! https://www.ft.com/content/8a96c13e-2623-11e9-b20d-5376ca521... - for example.
https://thepointsguy.com/news/virgin-retires-747s-closes-lgw...
But even the objectively superior business class on QR's new planes can't compare with climbing the stairs to the top deck, sitting in 64A [0] with the table and bins next to you for your flight. I first did this in September 2012, on a flight from Moscow to Heathrow. While we were coming in over the North sea I gave the at-seat phone a go -- it still worked (I think they were removed from service a while ago), certainly an experience at the time to be able to talk to someone from mid-air.
My wife and I had a weekend to Seatle in 2014, and bagged seat 1A and 1K at the very nose[1]. I think the 747 is the only plane you can get where you fly in front of the pilot (the A380 cockpit is at the front), and a unique experience.
I wasn't really flying when Concorde was around, and I've always regretted not flying it, but I'm glad I managed to experience both the upper deck and the nosecone on a 747.
(Oh yes, BA's 747 was one of the few planes I've flown on with a window in the toilet)
[0] https://21stcenturyjourneys.files.wordpress.com/2010/09/dsc0...
[1] https://scottmcgee.files.wordpress.com/2010/10/11-ba747-larg...