Once...
I got to sit upstairs in a 747.
Flying back from Detroit I checked in early due to the availability of a lift to the airport for a BA flight. Unfortunately the project budget didn't run to Business Class (even though we were entitled to it under Company rules) but BA had a couple of 747s with Cattle Class upstairs. Being early and looking fairly respectable I was offered a seat up there. It was cosy but they only allocated 2 of the 3-across seats and we had our own very attentive steward. The only downside was whenever anyone went to the facilities they had to brush past the pull-down projector screen (Titanic was showing, which dates when this was).
Crossing the Atlantic every week for several months was sheer hell but I've got a few stories from the experience such as probably travelling on the fastest every DC-10.