I agree, that's something I like about the movie in general, it's flows in an exceedingly natural way, there is absolutely nothing arch about it and it's beautifully done.
However, that 'reality' that is brought to the film bothers me in the context of Elizabeth Bennett's character. Knightley is very naturalistic, she acts just like any girl would now, faced with such situations. It makes her seem like she's at the prom, giggling and laughing with her sisters over dumb stuff, and not a whit smarter or more interesting than any other girl, or her sisters. She could be anyone, a girl who lives down the street from me. I don't actually see any of what I think Elizabeth Bennett should be, which is miles above everyone else in intellect and good sense. Yes, she's pretty. They've tried so hard to find a modern audience, to relate the feelings in the story to the way anyone might feel in such a situation that they took the specialness, the smarts out of Elizabeth. I just don't see Knightley as exceptional, which for me anyway, negates the whole premise of the book. I'm not saying Knightley is bad, what she does is well done, but to me, she's not Elizabeth Bennett, it's a different story.