We were in Section 453 -- not good seats, but we were there. It was near the split of the two sections, so there were a lot of ND fans nearby.
Had no problem with any of them. They were loudly supporting their team before kickoff, but heard no smack, just them cheering for their team. Got quieter as we marched on them in the first quarter, and were stunned from the first play of the 2nd quarter on. Most stuck around for the whole game, and were congratulatory and sportsmanlike on their exit at the end. They didn't stay for the presentation of the trophy, but I wouldn't if I had been in their shoes either.
Saw only one person wearing an obnoxious shirt -- the Catholics vs. Cousins one.
Did see a heavy majority of ND fans outside the stadium...easily 65-35. But I'm told that a lot of ND fans came without tickets, with no intention of actually attending the game. Inside the stadium, I would have said a slight ND advantage. Maybe 55-45 / 60-40 ND.
Just my observations.