This is a Node.js app which uses the Facebook Graph API to download recent posts from 1 or more groups, and display the top posters, top commenters, and their stats in a leaderboard-style format. In production, I use this app to keep track of some groups I admin with thousands of users each, and make sure that no one is unnecessarily spamming the group.
Live Demo: http://www.dmuth.org/facebook.
The source can be downloaded from here:
Give it a try, and let me know what you think!