Facebook is looking to increase sign-ups by adding a competitive element to inviting friends to the site. By clicking “Who’s here because of you? Track your invites” in the bottom of the right home page sidebar, users can now access Facebook Impact, a leaderboard that shows which of your friends have gotten the most people to sign-up for accounts on the site. Under the headline, “Facebook is best with friends”, the page also provides a custom invite link users can share to boost their ranking, and an “Invite More Friends” button that pops up the email contact importer and inviter.

Accessible at the URL http://www.facebook.com/impact/, as well as from the Get Connected section of the home page, this referral leaderboard takes cues from online poker sites which have long used referral bonuses and leaderboards to expand their user bases. Other social networking services have also provided similar features; with some effort, users of custom social network platform Ning can create referral leaderboards, for example. Facebook is making this feature easily accessible to everyone.

Impact shows you the profile pictures of your 9 friends with the most accepted invites sent and your ranking amongst your friends. Human silhouettes represent the number of invites you’ve sent, and profile pictures are displayed for those who’ve accepted your invites. Facebook hopes the desire to increase one’s rank and see those rows of icons fill up will encourage users to invite everyone they know. In areas where Facebook is widely used, this feature may initiate enough invites to wear down and convert the last hold-outs from the site. Simultaneously, in rapid growth areas like Brazil and the Pacific Rim where there are plenty of people to sign-up, Impact’s game mechanics might lead users to become addicted to inviting their friends.

In order to track these invites in greater detail, Facebook has also activated the Invite History feature at http://www.facebook.com/invite_history.php. Users can navigate to this feature by clicking “Who’s not on Facebook? Invite them now” in the Get Connected section of the home page’s right sidebar. Once on the Invite Your Friends page, users will see a “View All Invites” link that allows you to “See your entire history of invitations, including who has joined because of you”. There, users can see who they’ve sent invitations to, when they were sent, and whether or not those invited have joined yet. The page also allows reminders to be sent to those with outdated pending invitations.

Facebook’s recent focus on invites, demonstrated by their acquisition of the Octazen team, comes at a time when the world is watching their sign-ups and traffic rates closely in the wake of fallout from privacy issues. Impact, which can help boost these metrics, may be helping to offset any reduction in rate of growth due to the uproar surrounding changes to profiles, instant personalization, and the open graph.