On interracial marriage (or relations) Steve Sailer has an article up on this issue. In particular, check out this paragraph:

It's at least arguable that the mixing of various European nationalities that has been going on in America for generations, especially since the immigration cutoff of 1924, has been more important than the much more limited mixing of different continental-scale races that began a few decades ago. When you peer closely enough, white Americans just don't look that much like Europeans anymore, apparently due to genetic blending among white Americans.

So true! A few years ago, I remember the supermodel Vendala telling Conan O'Brien how diverse Americans were physically. She complained that all women in Sweden looked like her (to which Conan quipped that he had an urge to move to Sweden!).