Facebook integration

There's code already checked in to help implement hook_node_access_records, so that permission to view content can depend on a user's friends and groups. Right now, to make use of it, you'd have to define your own content type and implement some hooks. http://apps.facebook.com/secretboard is a working example. So this is possible, but takes some work to set up.

But don't assume that every application wants to limit access. When you post to this site, its like posting to a public discussion board on facebook. Anyone can see the post, not just your friends. Some apps will want content to be visible to everyone, some only to registered users, and some to friends. Drupal already has ways to address these sorts of issues and I'm not interested in re-inventing those wheels.