I like how Rowling handles the theme of truth.
Harry is obsessed with getting the truth, getting answers, all through the last several books. He wants to know who's good, who's bad. Like with Dumbledore, in DH. He scoffs when Doge, and later Hermione tell him not to let anything tarnish his memory of Dumbledore. Because Harry doesn't trust his own experience, he is obsessed with gaining facts.
And he gets facts, in the end. And even if they seem at odds with his experience of Dumbledore, Harry is able to make that information fit with his experience and he comes out with a much richer sense of who Dumbledore was. The fact (hah!) is that Harry's gut feeling was, more or less, right. "The truth" didn't alter who Dumbledore was.
The conclusion of the tale is not that things are black or white, but rather the reverse - Grindlewald, Doge, Snape and Aberforth all had very different experiences from dealing with Albus, but in the end, the story doesn't deem any of those experiences "truer" than the next. And I like that. I like that she allows Harry (and us) to realise that facts only go so far.
But what was up with occlumency not going anywhere? Rowling kept going on about it for the last three books, but Harry never learned it, and never was any worse for it (er, except for the whole thing about Sirius. But we all thought that Sirius was just the top of the terrors-of-not-knowing-occlumency-iceberg. Then nothing happened.)
Hermione keeps nagging throughout DH about it, but nothing comes of this.
I'm quite sure that Chekhov made a rule about this not being allowed...