Better go check your Facebook profile pic to make sure it's suitable for advertising—the company has begun using real users' postings in ads being shown to their friends. The effort is eerily similar to parts of the now-defunct Facebook Beacon, but Facebook is now calling them "sponsored stories," and users won't be able to opt out of their posts being used to advertise to friends.

The new "feature" started showing up quietly on Wednesday morning without any kind of fanfare from Facebook, but users began to notice it right away. Things posted by their friends; check-ins at businesses and "Likes" clicked from other websites started being highlighted in the right-hand column with the other ads, under the headline of "Sponsored Story."

Facebook says that the new ads are an effort to help marketers take advantage of what people are saying about them online. "Currently, marketers don't have the ability to know or plan word-of-mouth endorsements as part of their campaigns," Facebook's product marketing lead Jim Squires told the Wall Street Journal. "This gives a way for marketers to increase the visibility of stories about their organization this is word-of-mouth marketing at scale."

The company has reportedly been testing the feature for months and claims to have seen a positive reaction from users, who apparently prefer hearing about things from their friends rather than a faceless entity.

Still, there are ways in which the system could be improved, especially for those concerned about their privacy being respected. The most obvious is that users are not notified that their posts are being used in ads, and cannot block their posts from becoming ads unless they change their privacy settings to make the posts private. That's one thing Facebook has going for it this time around, though—the company will respect all privacy settings so that only the people you've already authorized to see your posts will see ads with you in them.

In some ways, the sponsored stories are a refined version of the disaster now known as Facebook Beacon. Launched in 2007, Facebook attempted to achieve basically the same goal by offering marketers a way to capitalize on users' off-Facebook activities by publishing purchases to users' walls. This resulted in a class-action privacy lawsuit and Facebook eventually shut Beacon down as part of its settlement.

Now, users' off-Facebook activities are basically part of the Facebook ecosystem thanks to "Likes" published all over the Web. If you click the Facebook Like button on any given site, that data is transmitted to your own Facebook profile and can be promoted by marketers in ads to your friends. We knew something like this was coming—it was rumored last year in advance of Facebook's f8 conference—but it's still fascinating to watch the evolution of Beacon and the very different reactions this time around. There are certainly users who are unhappy with their check-ins and likes being used to generate more cash, but the privacy concerns appear to be mostly gone—for now, that is.