From the Q&A that was linked by nethwen further up this page, plus comments.
-There was some speculations/impressions about Sherlock's reaction after Magnussen showed an empty room instead of the expected vault.
Not saying it closes the subject but this is what the director said:
''To have an episode where Sherlock Holmes makes one or two mistakes, you witness him realising these mistakes he keeps making. A terrific, terrific project to be involved with.''
-Many asked why Sherlock didn't react more at the word 'liar' he saw in his mind when he meets Mary. I like this answer; doesn't satisfy me completely but i like it:
''I think the frightening thing about Sherlock Holmes is that he actually is human, he’s completely human, and he has all the impulses and the feelings that every other human being has, but he suppresses them in order to be a better detective, and it’s on those moments where he doesn’t successfully suppress it that he gets into trouble. He believes that emotion gets in the way of his brilliant brain, and on the evidence of the show so far and of the original stories he’s completely right. When he gets emotional, he gets blind. He doesn’t spot Mary as a fraud as he should have as she points out in that episode. Ages ago, he should have spotted it. You know when you see the word ‘Liar’ all around her – as some people have noticed – when he first meets her there’s a whole blizzard of words and one of them is liar and he ignores that word because he wants to like her.''
That's just from the first quarter, there's plenty more. Last exemple, i said i liked what Moffat said, some other answers, i didn't like as much. Quit interesting!