Horcruxes, or at least Voldemort's penchant for magpipery is emphasised in Dumbledore's summary of the scene in the orphanage.

Also, I wonder what happened in the cave. I suppose the effect is heightened by it not being spelled out. She leaves it to our imaginations.

Regarding writing: Rowling is still interpreting for us. Dumbledore's summary of the scene (Voldemort's reaction to the name "Tom", his self-sufficiency and lack of friends, and the magpipe tendency -- it's as if she's worried we'll forget that he is who he would grow up to be.

Another puncturing of a tense moment as a bird drops its ... contents at Seamus' head while he is staring disgruntledly at Harry.

Luna's comment that Scrimgeour is a vampire is insane on the surface, but the sentiment is quite accurate. He is preying on people he should not prey on in order to keep himself in power.

I have no explanation for the idea that aurors are trying to bring down the ministry through a combination of dark magic and gum disease.

The conversation between Snape and Draco is riddled with plot development. A red herring in Draco's assertion that he had nothing to do with the necklace (showing that Snape is not in his confidence, if nothing else), but also that he is definitely hiding something (the occlumency -- interesting that Draco could learn it when Harry could not). And Snape pretending to be on his side (where would I have been if I had not known how to act). How Malfoy is aided by Crabbe and Goyle (and the more subtle clue that Snape is sabotaging that).

Sanguini: I like him as decoration. The edging towards the group of girls and being handed a pasty.