One interesting development I've noticed is the growing prominence of whites representing black countries, most notably swimmer Kirsty Coventry, who represents Zimbabwe (she's lived in America since college, although she retains a slight Rhodesian accent -- she pronounces her American college Auburn as OW-burn). She's won seven of Zimbabwe's eight medals in history.
I've seen other whites representing West Indian and African countries as well. Some of them live in those countries, some are presumably claiming ancestry by descent. It's often easier to get to the Olympics as the sole representative of Tanzania in your sport than by making the British or Australian Olympic team, which is typically limited in number (e.g., a maximum of three from a country in track events).