We get to know that Harry's experience of the Sorting Hat considering more than one house is not an isolated incident (with Hermione almost ending up in Ravenclaw). I like this, mainly because it makes clear that people aren't types, that there are facets to their personalities. This ties in with the bigotry theme, of course: bigotry is based in generalisations, and the good guys keep showing awareness that the world is not as clear cut and simple as all that.

Am I right in thinking the Giants are in the Urals?

I like the idea of Giants as an endangered species. The parallels are there: humans (wizards in this case) have killed a few, but more importantly they have forced them into an unnatural way of existence which makes them die off. It ties in with the bigotry theme again, but differently: it is not so much about unfair stereotypes (the stereotypes here seem to be fairly accurate), as it is about wizards' rights to subsume the rights of other sentient beings to their own comfort.