I had an interesting experience this week. I currently have 998,100 lifetime miles. This week I flew back and forth IAD to LAS on an award ticket.
I guess the flight and ground crews get some warning that your million mile threshold is coming up, because on the outbound, the FA serving drinks said something like "Sorry for waking you up mister million miler! Thanks for all your business and congratulations". On the return flight, I was sitting in my exit row aisle seat at the gate and before push-off, someone comes back and asks if I was Mr Biggreg. I said yes, and she said "Hi, my name is Cookie. I'm the customer service lead here and I wanted to congratulate you on reaching a million miles on United" I said thanks, and she continued "Do you mind if I take a picture with you?". I said "Uhhhh sure I guess", and she pulled out her phone, crouched down next to me in the aisle, and asked another passenger to take our picture! I sort of wonder where that picture of me about to fly a red-eye after a long day ends up, but it was interesting.
Since both these flights were award miles, my lifetime total hasn't changed... I guess we'll see if I get a third acknowledgement on my next paid flight when my lifetime miles actually tick over 1 million.
I didn't get any special perks or treatment, but it was kinda of nice to be acknowledged.