One of the ways that the Democratic campaign could end almost immediately is that Hillary Clinton could get polled to death. If the tracking polls over the next couple of days reveal a significant bounce for Barack Obama, that will signify that the electorate has made its choice and is prepared to move onward to the general election.
On that front, the news from Rasmussen is good for Barack Obama. He leads Hillary Clinton by 8 points over the four days of their tracking poll, but by 11 points in the two days of interviewing since the North Carolina and Indiana primaries were completed. In the 14 tracking polls that Rasmussen released in the interval between Pennsylvania and North Carolina, Obama had led Clinton by an average of 3 points.
EDIT: One unrelated point that's probably not worth a post unto itself. The Obama campaign has one more vulnerability in this race, which is that the results of West Virginia are going to be much worse than most of the media seems to understand. We're talking a 25-point loss if he has big momentum coming out of North Carolina. That's on a good day. On a bad day, he could lose by 40-50 points. Congressional Districts throughout the Appalachians that are similar to West Virginia have gone to Clinton by 2:1 or 3:1 margins.
As such, the Obama campaign will have to fend off one last bad (though almost certainly not terminal) news cycle. And therefore, I'd expect them to hold back any truly huge superdelegate endorsements (Edwards, Gore) until that time. This is not based on any inside knowledge; it's just too logical a strategy for things to proceed any other way.