Corrected entry: When Ron, Hermione, and Harry are looking at James Potter's seeker plaque in the trophy case, a similar crest next to his says that McGonnagall was on the same Gryffindor Quidditch team - the movie leads you to believe she was pretty old. That means, by my reasoning, that she would have been at least 20 years old when she started playing for the Gryffindors in the 1970s.
Corrected entry: In the scene where the troll has just gone into the girls washroom, Hermoine quickly goes back in to the 1st stall on the right hand side, but when you see the above view she is in the 3rd from the right. (01:07:23)
Correction: The overhead shot of her shows that she has her feet in the second cubicle from the left, most of her body in the third cubicle from the left, and her head just in the fourth one. She is crawling from one cubicle to the next. When she emerges, a few shots later, she has crawled up almost to the end of the cubicles.
Corrected entry: At the end of the movie Hagrid gives Harry the photo album. After Harry looks at it and tells Hagrid goodbye, he walks back to the train with his hands at his side and there is no sign of the album in either hand.
Correction: He could just put in one of the pockets of his robes.
Corrected entry: In the scene in the Great Hall where Ron is looking at his Chocolate Frogs cards, Harry picks one up. It's suppose to be Dumbledore's card, but in several shots you see where Dumbledore's picture should be. Instead, all you see is the green screen attached to the cards.
Correction: Dumbledore's picture was a simple holographic foil image; the same kind you'd see on any credit card. There was no green screen effect needed for this. What you're seeing is just the way the light plays off the foil when viewed from an extreme angle.
Correction: This might be a different McGonagall, or a child of Professor McGonagall, for there's no evidence that this is the McGonagall currently teaching at the time.