I achieved MM this past week on my flight segment SFO-ORD. (Brief pause for Kermit flail.) The purser come back to me in E+ (failed GPU upgrade, sigh!), confirmed my identity, then congratulated me on hitting 1 million during the flight. Then one of the FAs for my cabin came to me with her congratulations and asked if there was something she could get me, like some of the "good wine" from up front. :-) So my perks were a glass of sparkling wine then a glass of white, and a bowl of nuts. I don't think it was announced over the PA but I had my headphones on much of the time.
Coincidentally, the guy in the window seat said he was about 20K from MM so he was interested to see what might happen when he hits hopefully in the next few weeks.
Interestingly, I also got congratulated by an FA on my next flight ORD-DEN, even though I was about 900 miles past 1 million at that point. An old and close friend was on this flight with me for a family related reason, using an award ticket from me as she went from 1K to no status when she changed jobs in her company and had not flown even for personal reasons in a long time. She was very happy for me though it just reminded her how far she had fallen, FF-wise. (I think she had made it only to about 700K lifetime when she stopped traveling.)