Described in this useful Times piece:
But Mr. Plouffe said the volunteer program was modeled after the one Mr. Bush’s aides devised in 2004, which sent supporters door to door to spread the word about Mr. Bush in their own neighborhoods — a personal touch informed by detailed lists of neighbors’ occupations, voting histories, pet causes and hobbies.
Four years ago, Democrats and their liberal allies scrambled to match the vast lists of personal voter information gathered by the Republicans through public records and consumer data banks.
The Democratic National Committee has since greatly improved its voter information file, which is now at Mr. Obama’s disposal. But Mr. Obama’s aides were also considering buying another huge list with information on 230 million Americans. The list is owned by Catalist, a private concern co-founded by a longtime Democratic operative, Harold M. Ickes.
In an interview, Mr. Ickes said that Mr. Obama’s campaign aides are particularly interested in new information his company has gathered about cable television viewing habits.
Obama campaign officials said that is because they are considering a specially tailored commercial campaign on niche cable networks like MTV, with its young audience, or BET, with an African-American viewership Mr. Obama’s aides consider crucial for victory.
I think a lot of people have the mistaken impression that Hillary lost because of Mark Penn's obsession with microtargeting, in contrast to the big-themed, macro-focused Obama campaign. But pretty much everything about that statement is wrong. First, the Clinton campaign had plenty of big ideas--that experience and toughness are key presidential attributes, that everyone should have health care, that we need to withdraw from Iraq. The problem was that Obama had many of the same big ideas, and, in the places where they differed, Obama's were slightly more popular.
Second, the assumption that campaigns face some sort of either/or proposition--that you either microtarget or deal in Big Ideas--is deeply flawed. Most successful campaigns do both these days; they're two largely-separate parts of the effort. The ideas are the substance of the campaign, the microtargeting is procedural--the way you convey your ideas.
So, for example, one of Obama's big ideas is the we should do something about global warming. Since young people tend to be especially concerned about this problem, you'd probably stress that idea when communicating with them. And one of the most direct ways of communicating with them is to place ads on the cable channels they watch or in the magazines they read--i.e., microtargeting.