As in the last election, both campaigns used Facebook, Twitter and other social networks, but this time they moved on to the targeted advertising we are now used to on the Internet -- white males saw different campaign ads than their wives. (See articles in both The Economist and The New York Times.
Perhaps Obama was a more aggressive in tracking clicks than Romney. The Times checked Obama and Romney's Web sites during the campaign, and found that Obama was using 76 click tracking services and Romney 40. I checked yesterday and found that Obama was down to 32 and Romney only one (click on the image to the right to see which ones).
A couple of factoids to establish context:
The Economist quotes Borrell Associates as estimating online ad spending in 2012 at $160 million, six times what it was in 2008, but it remains a small percent of the estimated $6 billion spent on the election.
This understates the impact of online campaigning, because it costs very little -- the Obama campaign built about 200 different programs that ran on Amazon's cloud services.