The social media giant Facebook recently rolled out some changes to how it’s 500 million users will experience the web. Not just what users will see on Facebook.com but what they’ll see – and do – on lots of other sites as well. For examples, just visit your favorite movie site on IMDB or some news story on CNN.com. On those pages, and many others, you can choose to “like” or “recommend” what you see. That information is stored and organized by Facebook, which plans to use it to bring you new social information about the world and what your friends think of it and to serve up more specific advertisements. But the changes make some critics nervous about privacy issues, especially because all of these new features have been implemented as “opt out” features, meaning unless you choose otherwise, you’re signed up. We talk with Mark Kirkpatrick, author of the forthcoming book The Facebook Effect.