One of the CNN commentators this morning said that a lot of the debate-watchers who said Obama won are young Democrats. You could interpret that as Obama "preaching to the choir." But something else jumps to mind:

One of the things the GOP did right in 2004 was to make a big push to register new voters, most of whom voted for Bush. Bush's popular margin was 3% over Kerry, which doesn't sound huge--but it represented a 3 million-vote plurality, which is pretty good. Obama's people have registered a large number of new, young Democratic voters, and the debate polls may be an indicator of things to come.