The District of Columbia held its primary this year on April 3. It was a combined presidential primary, and a primary for all other partisan office. According to this story, only 15% of the registered voters cast a ballot. City councilmembers are already talking about moving it to June in future years. See this story.
It is tough, because their is little, if any real Democratic Party primary, and the overall tone from the press is that the GOP primary is basically over and it will go to Mitt. How many of the GOP candidates spent much time or money in DC?
It is one of the reasons that States often move their primary to an early date, believing that it will make the State more relevant and thus increase voter turnout.