In the last day or so, you may have noticed a barrage of Facebook status updates reminding you to go vote. You may even have posted one of those status updates yourself. And you’re not alone — more than 1.6 million users “donated” their Facebook status to the Causes application for a virtual get-out-the-vote rally. The Causes Election Rally has only been online since last Thursday, so we’re talking about a growth rate of tens of thousands of users per hour.

[Update: It’s Wednesday morning, and Causes is announcing 1.75 million people participated, making it the largest online rally in history. Assuming those 1.75 million voted, the participants made up in excess of 1 percent of the overall U.S. popular vote. That’s impressive, but not quite enough this time to have actually made the difference, given Obama’s wide victory margin]

Causes founder Joe Green sounds pretty happy with how things are going — he says this is the first election in years that he hasn’t spent involved with get-out-the-vote efforts for political campaigns in battleground states, but I’m guessing that staging an online rally on this scale is a decent substitute. Here’s how it works: Users could sign up for Causes to change their status update at midnight today to tell everyone to vote, plus they could schedule other reminders throughout the day.

The hope, Green says, was for users to log into Facebook and just see a steady stream of voting reminders in their news feed, which would increase the social pressure to vote. There are plenty of other news feed marketing campaigns, but tying the message to your Facebook status gives it some extra oomph.

“It’s the closest thing Facebook has to standing up and yelling on a soapbox,” Green says.

Green also shared some estimated data on the kinds of status updates that people used — you could choose a nonpartisan get out the vote message, a pro-Barack Obama message, a pro-John McCain message or something personalized. More than 1 million people went with Obama, 350,000 chose a McCain endorsement and 125,000 used the nonpartisan update. That may seem heavily skewed towards Obama, but McCain actually did better than he does among the overall Facebook audience, where Barack Obama has 2.4 million friends and McCain has 630,000.

“Obama is only beating McCain 3 to 1, which I would say is actually pretty good [on Facebook],” Green says.

He adds that among the personalized messages, many users chose to say “No on Prop. 8,” the California ballot measure that would ban gay marriage.

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