I thought the Mudblood/Pureblood whatnot, especially the Chairs of Doom at the Ministry, were very Holocausty. And I think it's interesting that that kind of eugenically driven violence is what JK decided was guaranteed to jerk revulsion out of a modern audience (I do quite like HP, but it is very much mass entertainment) - eugenics was pretty accepted globally and in the US in particular pre-WWII (esp. in the '20s), and Hitler kind of changed all that and made eugenic sentiment the height of evil forever. That was my primitive sociological observation of the book.