I can’t remember if was in the movie or not, but there’s a scene just after Ron and Harry both get shot down asking girls to the ball. Ron turns to Hermione, and a realization slowly dawns on him:
“Hermione! You’re a girl!”
Camera tricks and a very large body double with a realistic face mask. I saw some shots of him in an online collection of set photos for Order of the Phoenix. Weird to see Hagrid with his head under his arm. 
That was the first I knew of the body double. Now I make a game of picking him out when we watch the DVDs.
Rowling is on record stating in interviews that the character she identifies most closely with is Hermione. Who is also over-perfect in some ways, so I suppose you could make a case for her being a Mary-Sue. But Rowling’s a lot more nuanced in her writing than the typical fanficcer, so I won’t try to make that case.
Hagrid is the Groundskeeper (along with a few other titles: He’s also “Keeper of the Keys”, and, now, the teacher for Care for Magical Creatures). Filch’s job is (I think) listed as “Caretaker”. The division of responsibilities seems to be the castle walls: Hagrid takes care of everything outside, while Filch handles the inside. As a completely irrelevant aside, there are hints in the book of a romance between Filch and Madame Pince, the similarly-unpleasant librarian.
I know this has been answered a couple of times already, but I’m going to expand on it a little more.
At the end of Goblet of Fire, Harry hears Voldemort in the cemetary addressing some Death Eaters by name. When he sees the Minister of Magic (Cornelius Fudge) and attempts to convince him that Voldemort is back, Harry says “Here are the death eaters that were there! Crabbe, Goyle, Nott, Malfoy” etc.
The minister says “You’re just saying names of people accused of being Death Eaters in the past but were found to be innocent.” Implying that Harry could have found those names in old Daily Prophet articles and fingered them as likely suspects.
In addition, Lucius Malfoy in particular is rich and has many influential friends in the ministry obtained through donations to Ministry causes, invitations to dinner, etc.
This is why Malfoy, though being “outed” by Harry, is not arrested. Though, of course, in Order of the Phoenix, …
Another question that just occurred to me:
13 - Does Ron ever successfully cast a spell? Aside from the scenes in which he tried to use his broken wand in CoS, I don’t recall seeing him ever even attempting to cast a spell. Even his scene with the boggart (in Professor Lupin’s class) didn’t seem like he was actually casting a spell; since Prof. Lupin had already explained the the best weapon against a boggart was laughter - pointing the wand and shouting “ridiculous!” seemed like more of a mnemonic device of sorts to help the wizard think of something funny.
Heck, even his attempts with the broken wand seemed to be little more than a setup for Lockhart snatching his wand later in the movie - as if they first wanted to drill it into the reader’s/viewer’s head that the broken wand would cause spells to backfire (the old “pistol on the mantelpiece” thing).
Perhaps Ron is just very subtle about his spellcasting and I simply didn’t notice his successful spells?
And another silly question:
14 - Does the Gryfindor quidditch team ever play against anybody but the Slytherin team?
(Order of the Phoenix spoilers)
Apropos of nothing, one of the things that I find most irritating about the series (though I love the books) is the extent to which the entire plot of HPatOotP revolves around Harry telling a story which no one believes. In fact, there are at least two ways that the Wizarding community ought to be able to verify Harry’s tale, either Verita Serum or by looking at his memories in one of those memory pools. Now, maybe there are fanwankable reasons why one or both of those would not work, but they certainly ought to be at least discussed.
They do a good job making Hagrid big in the movies, but he isn’t big enough. In the books, he’s regularly described as “twice the height of a normal man.” That puts him at ten or twelve feet.
I wonder how big they’ll portray Grawp, the ‘small’ giant. In the books he’s sixteen feet tall. 'Course, he could have been left out when they scripted Phoenix–anyone heard if that sub-plot made the cut?
[spoiler]Logically of course that would work, but even with the word of Dumbledore, the most trusted wizard in the world, the ministry is adamant about refusing to believe Voldemort is back. Voldemort’s return would mean the ministry would look weak, so they do everything in their power to make sure the public is unaware of it. If Harry took verita serum (they could just say well of course Harry really believes his own mental delusions) or had a penseive memory, they could just refuse to look at or acknowledge such evidence.
It might seem contrived and far-fetched, but looking at how the US government convinced its populace that Saddam bombed the twin towers, the whole thing is frighteningly plausible.[/spoiler]
“Riddikulus” (I think that’s close to Rowling’s word) is an actual spell. Us non-wizards would have no way to do that boggart trick.
If you’d watched the first movie, you’d have seen Ron attempt to learn to levitate objects, and do it sucessfully when it really counted, saving both his friends’ lives.
But I agree, Ron often isn’t given enough to do. I hope his strategic mind has some impact on the last book. He was a chess prodigy in the first book, but it hasn’t come up since.
They were playing Hufflepuff in Prisoner of Azkaban when the dementors caused Harry to pass out. It was the first time he’d participated in a match that his team didn’t win. I don’t recall if it was in the movie.
Phase42: in the books, matches against any / all of the other Hogwarts houses take place and are described.
MaxtheVool, Yumblie - the two methods mentioned by MaxtheVool to prove that Harry is not lying are both methods that we know can be “tricked” in the magic world.Slughorn fakes the pensieve memory given to Dumbledore; Dumbledore or someone else explains how someone can fool veritaserum through the use of advanced magic.
I think the implication there (and then later on, at the beginning of the next book) is that it’s not a case of Ministry knowing he’s lying, just that they don’t want the truth to get out. Fudge likely knows that Harry isn’t making it up - he’s just providing excuses without really believing them. That’s why they don’t give Harry veritaserum/use Legilimency, because those things would confirm that he’s telling the truth, which would look very bad in the papers.
Fine. But that should be discussed or mentioned, rather than Harry saying “hey, here’s some incredibly earth-shattering news which everyone in the wizarding community needs to hear” and the powers that be saying “he’s lying” and that being that.
I saw the first movie several years ago, or at least part of it, but I’m afraid the only part I remember was the “Every Flavor Jellybeans” scene, in which Ron gets the vomit-flavored bean 
I think I’m gonna have to read the books. My sister has them all, I think, so I’ll hit her up when I’m finished with my current stack.
Since this thread is about the movies, and I don’t particularly want to start a new thread, here’s a bit of news: David Yates, the director of Order of the Phoenix, is now signed to also direct Half-Blood Prince.
Link to the article that says it, which also talks about filming Order of the Phoenix. No major spoilers, though it does talk about some important scenes, so for those who are spoiler-phobic, you might not want to click if you haven’t read the books.