TR has an amazing (and long!) article in admiring detail about how Facebook runs experiments on its users regularly:

"Our goal is not to change the pattern of communication in society," he says. "Our goal is to understand it so we can adapt our platform to give people the experience that they want." But some of his team's work and the attitudes of Facebook's leaders show that the company is not above using its platform to tweak users' behavior. Unlike academic social scientists, Facebook's employees have a short path from an idea to an experiment on hundreds of millions of people.

In April, influenced in part by conversations over dinner with his med-student girlfriend (now his wife), Zuckerberg decided that he should use social influence within Facebook to increase organ donor registrations. Users were given an opportunity to click a box on their Timeline pages to signal that they were registered donors, which triggered a notification to their friends. The new feature started a cascade of social pressure, and organ donor enrollment increased by a factor of 23 across 44 states.

Marlow's team is in the process of publishing results from the last U.S. midterm election that show another striking example of Facebook's potential to direct its users' influence on one another. Since 2008, the company has offered a way for users to signal that they have voted; Facebook promotes that to their friends with a note to say that they should be sure to vote, too. Marlow says that in the 2010 election his group matched voter registration logs with the data to see which of the Facebook users who got nudges actually went to the polls.

We are all guinea pigs in Facebook's laboratory.

I wonder if, years from now, people will wonder why we gave Facebook access to so much of our data.