In 2004 the field operatives on the Democratic side were the DNC itself, independent groups, and labor. They got beaten quite soundly by the RNC, largely because the RNC refined their system (and yes, four years later you should still read this story) while Terry McAuliffe wooed big ticket donors while the DNC's ability to operate anywhere beyond the swing states was in question.
This year, the nucleus of Democratic field work is going to be the Obama team, which so far is just about the best in the party's history. In all likelihood they will be supplemented by the people on Sen. Clinton's team with a clue (they exist). The DNC has recovered from '04 and is now ready to compete on a much wider scale - in 2006 and this year they've shown they are more than capable of running in red districts, and know how to turn out Democratic voters statewide. And of course, labor will be on the ground as they always are.
I say this because the McCain field team is infested with Giuliani people. Yes, the Giuliani campaign that got out-organized by all their Republican compatriots. Also remember that McCain lucked out with his New Hampshire win, and ended up the nominee after everyone else just turned the GOP electorate's stomach. They haven't been activating voters while the Obama/Clinton fight has turned out voters for 6 straight months - Democrats and Independents - at numbers in some cases above their 2004 general election level in primary season.
And all that organizing will require money. Most of Obama's donors have not come anywhere close to primary and general election limits, and a good amount of Clinton donors will come on board.
Yes, the Democratic party nomination process has been acrimonious and somewhat damaging. But I get the sense that John McCain is playing the role of Napoleon on the eve of Waterloo. And Sen. Obama? I Like Ike.