Although most pundits suggest that the Democrats are suffering from the extended battle for the nomination between Clinton and Obama, I think this is giving them a huge advantage in the national election. While Clinton and Obama still have legions of reporters and reports following their every move around the USA, McCain has become something of a footnote to the process after wrapping up the Republican nomination. In short, the amount of *free media* for Obama and Clinton is huge compared to McCain's exposure.
This will change after the Democrats pick a candidate and McCain and either Clinton or Obama start the "real" fight for the Presidency, but by then voters will be much more familiar with the Democrat and also will be suffering from campaign fatigue after a national process that started earlier and has lasted longer than any Presidential (or any other?!) race in history.