I sat behind Fabio (well, he was in 1B and I was in 2A) on a flight from PDX to MSP last December. It was much more entertaining for my Facebook friends than it was for me, though.
Also, stood about 8 feet away from Rob Reiner while waiting in SLC to board my flight to Denver last year. He was boarding a flight to LA. Some guy standing next to me points, and says "Hey, isn't that Rob Reiner right there?" I turned, and said "Could be. or Carl Reiner. Or it could be Penny Marshall - they all look the same to me."