Patrick Ruffini (via Ben Smith) has some fascinating thoughts about what makes Obama's ground organization so sophisticated. And, if you like that, you may also want to read this (very long) Zack Exley post on Obama's organization, which he observed up close in Ohio.
The gist: Rather than start off by building up a network of supporters, the Obama organizers around the country focused on recruiting volunteers, who would in turn go out and find the supporters. While this required a big initial outlay of time, it massively increased their capacity to round up votes. It's really perfectly intuitive: Recruit 12 voters and you've got 12 votes; recruit 12 volunteers and you've got 12 people who can each turn around and recruit 12 voters. But, because it requires a small leap of faith (and a ton of discipline), campaigns rarely do it.
As one of Obama's Ohio field directors told Exley:
We had a whole month where, on our nightly calls with headquarters, we did not report our voter contact numbers. We only reported our leadership building [i.e., volunteers]. I definitely stayed on top of what our voter contact numbers looked like. But headquarters wasn't paying attention to how many voters we registered or how many doors we knocked that day—they were paying attention to how many one-on-one meetings we had, house meetings, neighborhood team leaders recruited, how many people we had convinced to come to this wonderful training in Columbus that we had. Yes, it was definitely scary to see how big our persuasion universe [i.e., persuadable voters] was and know that our first priority was not to just be tearing through that.
Update: I'd be remiss if I didn't also mention Alec MacGillis's excellent piece on the same subject in yesterday's Washington Post. MacGillis cites another reason Obama has been able to implement this approach while other campaigns failed to:
Though the Obama campaign is modeled after previous incarnations, it was shaped and reshaped during the long primary season, as the team adopted what worked and shed what didn't. The operation took months building a network of support in Iowa that paid off with a crucial caucus win, and its belief in that sort of organization hardened when it lost a week later in New Hampshire, where it had done less organizing.
A breakthrough came with the turn to the neighborhood teams. Ganz had been testing the model for the Sierra Club, and the campaign tried it in South Carolina, to great success, as team members held one another accountable and boosted morale.