My first flight ever (in 1996 or 1997) was a massive delay due to a leaking battery on a wheelchair; I was upgraded to first class when they sorted everything out and rescheduled everyone. Talk about ruining expectations (I've never flown first class since).

I used to fly quite a bit from the UK to US and got upgraded a few times. I still remember getting bumped up to business on a place with full reclining seats that turned into a bed.

Come morning I slowly returned to upright and could see all the way down into cattle class - where I discovered that one of my colleagues had been on the same flight... he looked less than impressed.

Another time - pre 9/11 - I somehow managed to make it all the way through to boarding a day early for my flight. So they bumped me up a class to get me on the plane.