I just found this thread - very entertaining reading!
I've only sat next to 2 celebrities in my travels - both in J class in Asia.
The first was Thongchai Jaidee (not a major celebrity, but quite big in the Asian golfing world - probably the most famous golfer Thailand has produced).
A lovely guy and he actually started the chat and, naturally, we talked about golf, which is great for a total hack like me.
I also sat next to British TV Chef, Ainsley Harriott on a flight from SIN-HKG once in SQ J. A lovelier guy you couldn't ask to meet.
I knew who he was and wasn't going to disturb him, but we hit turbulence and he spilt his drink. Until the crew could get back with some napkins I offered him mine (which I hadn't used yet) and he was exceptionally grateful. We started chatting about a wide range of topics and he is just a fantastic guy.
We both established that we smoked (well, at the time I did) and he had run out before boarding and asked if he could "bum one" when we got to HKG.
As soon as we landed in HKG we made a bee-line for the smoking room. It worked out we were both staying in Kowloon in hotels near each other and he offered me a ride in his car that was waiting for him. A sincerely nice, warm human being.
My better half sat across the row from Gordon Ramsay once and said he was exceptionally rude to the crew for the whole flight. Surprise me.
Finally, a few months back I saw Luke Nguyen checking in for a VN flight from SYD-SGN. There was a problem with my booking that was in the middle of being rectified, and I was asked to "stand to the side" for a few minutes while they made a phone call. It was at this time LN turned up to check in. I didn't hear all of the conversation, but it did seem he was getting a little er...flustered... that he had been booked in Y class and wasn't guaranteed to get an upgrade based on "who he was".