It's addressed somewhat later in the novels. I think it is the second novel, but it is discussed in subtext throughout the book series, especially in the second book, and somewhat in the final book.
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He basically pulls the sword of fucking Godric Gryffindor out of the sorting hat to do battle with the monster in the Chamber of Secrets, and afterwards while recovering from injuries he asks Dumbledore if the hat made a mistake, remembering the "you would do well in Slytherin" conversation. Dumbledore basically then says... "uh, you pulled the sword out of the goddamn hat of the man your house is named after. I think it chose correctly" Basically, what that said to me was that the hat, while considering Slytherin, was basically seeing the taint of the mark that Voldemort left on Harry as a child. Plus, I think it is significant that Harry CHOSE to be in Gryffindor and didn't want to be in Slytherin, basically becoming the person he wanted to be rather than the person that might be the most popular.
I'd agree with the review that Radcliff and Grint have improved, although that isn't to say they're turning into "fine" actors. Radcliff is good with certain emotions; he can be mean, happy, angry, etc but can't pull off "sad" (ie his crying scene in PoA). I haven't seen OOTP yet, which will demand some emotion from Radcliff...
spoilers
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Although my brothers told me when Sirius dies, Harry acts almost indifferent and it's not treated like a big deal...