Reading Justine Larbalestier's post Damned if You Do, Damned if You Don't I have to say... wow. Really? In case you don't feel like clicking on the link, the basic point of the essay is that writers perhaps could/should include more ethnic diversity in their writing but if/when they try to do so they are likely to encounter a response from someone of that ethnic background who thinks they didn't get it right.
I'm not here to say that JL is right or wrong. My only feedback for anyone worried about this topic is - develop a more diverse group of friends and then you will accidentally write diversity. Because at heart all writers always write what they know, and trying to do something else will just make you sound forced. If you don't already have friends of color and varying sexual orientations then, seriously, get out more.
That's not to say that you can't write a character from a wildly different background than your own. But it's a good bet that if you decided to write about oh, say, a kid from northern Russia when you're from northern Virginia (USA), that you would spend a good deal of time researching that background and you would come to love that character. Love in the sense of opening your soul to blend with the information from your research and having it become part of you. Then your character will be pure and you will know it. You will know that you didn't set out to offend anyone (should they get offended), you just told the story that your young hero whispered to you.
My favorite quote from the comments is Karen David's stance that a character's race is "just a strand in their identity." That's just the thing, you see. A strand. Inherent in the design of the cloth. That's what my diverse friends are like. How about yours?