As a native of the upper Great Plains, I still pay attention to that area. As a North Dakotan, I am often mistakenly thought to be from South Dakota. People generally mix the two of them up. (Insulting, I know.)
Anyway, I'm surprised that Hillary Clinton won South Dakota in Tuesday's Democratic primary. I would classify South Dakota as a "lily-white state" - one with a minute number of minorities. A look at this map shows that other such states went to Obama. Examples include Idaho, Montana, North Dakota, Nebraska, Kansas, and Iowa.
The issue of Obama's church may have something to do with this. That wasn't really an issue when the other white states voted. Also, SD had a primary, rather than a caucus, which many of the above mentioned states had.
I would think it would be unsettling for Obama to lose a contest after the media has been calling him the winner for weeks now. But that isn't getting mentioned too much in the news.