On my last MR SEA-ORD which I upgraded with 500 milers (the first MR I've ever upgraded), the FA mentioned "It looks like your taking the scenic route", I think she could see my itinerary somewhere up front. She asked me with a big smile if I was doing it for the extra miles. I told her yes exactly, and she said "let me get your departing gate information for when we land!". She was very helpful and seemed to know exactly what an MR was... while I've never really found anyone on UA to be anything less than pleasant, she was really helpful and seemed pleased to have me riding up front...

edit:
I remember now, first she asked where I was flying today, and I said ORD, but we were headed to SFO. That's when she commented on the scenic route... so I guess I told her my itinerary...