Many of the registrants were on the younger side. The New York Times observes that 24 percent of California's registrations during the period came from 17- to 25-year-olds, and almost 30 percent from 26- to 35-year-olds.

The figures aren't completely surprising when this election marks the first for a generation of young adults that practically grew up using Facebook. Many of them are not only new to voting, but get a lot of their news from social sites. The real question is whether or not the Facebook campaign will have a meaningful impact on the outcome. That could be difficult to quantify, even in battleground states where a few thousand votes could make all the difference. Still, it's apparent that Facebook's get-out-the-vote effort is paying some dividends.