1. Harry nearly being Sorted into Slytherin. A lot of fanfic makes a big deal about this. As does Harry in CoS. So imagine my surprise when I reread book one, and Harry puts on the Hat, and *he's* the one who brings up Slytherin, after the Hat says he has traits good for more than one House. "Not Slytherin! Not Slytherin!. The Hat, having no antiSlytherin prejudice, asks him why, but puts him in Gryffindor. If Harry had not brought up Slytherin in the first place, I think it's possible that the Hat wouldn't even have argued.
2. Neville. I was reading Goblet of Fire, and I caught a classic bit of what I think is Rowling misdirection. She did that a lot in GoF, where we saw but ignored all the times bugs or beetles or insects just *happened* to be around. After all, they were in a garden, or by the lake or near an open window. Nothing weird about seeing a bug. Gryffindor is learning Banishing Charms. Flitwik has provided nice, light, soft cushions so that no one will be hurt. However, Neville's aim is, as usual, *off*. What does he Banish? We get the amusing sight of Professor Flitwik himself being Banished to the top of a cabinet, among other heavier-than-cushion objects.
However, the reader is, first of all, paying more attention to what the Trio are saying and second, just laughing at typical Neville incompetency.
But. Harry, when not concentating, can barely make his cushion flop over. And Harry is good at Charms. Here's Neville Banishing an adult (granted, a very small one, but still one who weighs significantly more than a cushion) and *other* heavy objects. And Flitwik lands safely.
And this seems to have started after he saw the Crucio. Which is also interesting. I think he was beginning to tap his true power. Because he seems to be very powerful in this scene.
3. Wizarding Families. Wizarding families seem to be in grave danger. Certainly the major pure bloods are - the Crouches are gone, the Potters and the Malfoys and the Longbottoms seem to be down to one heir. Cedric Diggory had no siblings, so unless his mother has another child, his family is doomed. The Weasleys have a huge family, but where are their cousins? I can readily believe that wizards have lower fertility than Muggles - they have longer lifespans and greater means of curing illnesses and injuries, or preventing them entirely, so it makes sense that they have fewer children.
The Weasleys are the exception, and this is known about them. "My father says Weasleys all have red hair and more children than they know what to do with." However - there were eight years between Charlie and Percy. This seems very odd, unless the Weasleys were deliberately not having children, and then decided that not having more kids would be giving Voldemort a victory or something. Or lost a couple of babies.
It also seems that Harry's Year is very small - only forty kids, all told, assuming that there are the same number of boys and girls in each House. It does seem that way - there are twenty brooms in the flying lesson with the Slytherins and twenty earmuffs in the potting mandrake lesson with the Hufflepuffs. It's possible that there is a different number in Ravenclaw, of course. Then again, Harry's cohort were born during the last of the War, so it's entirely possible that people were not having kids, and, of course, a lot of potential parents were dead. I'm assuming the Year after Ginny's is fairly large, full of celebratory kids.
Also. Only one all Wizard village in all of Britain, but given towns such as Godric's Hollow, it seems that there were others in the past that are Muggle now. And the one school, too, but I'm sort of assuming that there are people who just didn't make it into Hogwarts, and take jobs that don't require NEWTs.
There's also a lack of siblings - only Weasleys, the Patil twins and the Creevey boys that I remember. If anyone remembers others, please tell me. And the Weasleys are very fertile, the Creevey boys are Muggle born (interesting that there are two in one family. One random mutation I can buy; with two, I start to suspect wizard or squib blood) and the Patils are not only identical twins but we don't know if they're pureblood, half blood or (you should excuse the expression) Mudblood. The war was as hard on purebloods on either side as it was on nonpurebloods.
Which is interesting because Voldemort is a halfblood - more of one than Harry since Harry's mother may have been Muggleborn, but she was a powerful witch, while Tom Riddle, Sr was a pure Muggle.
Interesting, too, that one was sorted into Slytherin, and the other had it as a viable option (if not, the Hat wouldn't have joked about it.)
I'll do a spoiler post about OotP once I digest it.