I liked this article from Parenting which was written by the biological mom of an interracial child, and talks about how she deals with the constant questions she gets from strangers.  People just assumed that she had adopted her daughter, and would ask where she was from, and the author was surprised at how many people made this leap immediately without considering that there might be other explanations.  Her concern was ultimately for her daughter, in that she didn't want these constant questions to make her daughter feel that she was different, and therefore separate from the rest of the world.  Her resolution of how to answer the question is very funny.