The upper deck was really intended as a first class lounge and I think I was up there once. But obviously wasn't very economical and got turned into business class seating once that came in.
Qantas (I think, it’s possible it was BA) used the upper deck for economy and it was my favourite place to sit. The window seat had a little locker between your seat and the window (the curvature of the fuselage meant the seat couldn’t be right up against the window). It was a great place to keep all your stuff accessible without having to bother the aisle seat to get up to the overhead storage.