One month ago, we saw Facebook slip momentarily and expose a few unreleased methods to developers. The new methods, when combined, told us that there will be lists of users, and these have something to do with friends. At the time, I tried some input (did I have any “friends lists?”), but couldn’t get an interesting response back from the Facebook servers.

In a move pretty unusual for a competitive tech company, Facebook has confirmed our speculation on their What’s New page. “Sort out your friends. We’ll let you organize that long list of friends into groups so you can decide more specifically who sees what.” You could argue that they’ve revealed it to us because, unlike features worth hiding, this isn’t an innovative move. Instead, it’s a necessary one, and one for which they probably receive a lot of requests.

Since the story broke, we’ve learned a little more information. Here’s a recap of what we now know.

• What we know:
  • Friends Lists are like buddy lists, in that they are ways to group your contacts.
  • Friends Lists will be located at www.facebook.com/friends/. Before the publicity from the original story, a few users who guessed this URL got to see this feature in the works. The URL now forwards to your normal list of friends.
  • Friends Lists can be used for composing messages. The URL, when working, suggested this was the main functionality.

  • Friends Lists can be used as for privacy control. This wasn’t certain in the beginning, even though it’s a great, obvious feature. There was some fear that the lists might only be used for composing messages. The phrase “so you can decide more specifically who sees what” on the What’s New page verifies our hopes.

    Privacy has always been a founding block of Facebook. Their closed-network structure essentially made the site, and the News Feed backlash emphasized the sensitive role of privacy on the site. Friends Lists will be a perfect way to block your parents from seeing those wild photos of that trip you took on their charge card without telling them.

• What we don’t know:
  • Will we compose these lists from scratch, or will they be generated automatically from the current social graph features? When you add a friend right now, the functionality already exists to ask how you know that new friend. You can say you’ve gone to school with them, on a trip with them, hooked up with them, etc. I think that they’ll introduce something new, though, since the older feature isn’t widely used. If we’re lucky, though, maybe you’ll be able to import this information.

Since Facebook has already taken a month on this without releasing it, it’s safe to say this is a big feature. By naming it an upcoming feature, they probably don’t have plans to release it in the next few days, but my completely ungrounded guess would put the release somewhere between two and six weeks.