Years ago, as I was getting on a DL flight, I looked over the luggage tags in the first class section. The flight had five or six million milers on it. That's the first time I ever saw a "Twice as many is Twice as Nice -- 2 Million Miles" tag.

One guy had a tag that said "There can be Only One -- 8 Million Miles". I asked an FA about the guy. Yes, he was DL's most frequent flier. What did he do for a living? He consulted to airports.