How is leaderboard ranking determined?

The Participants leaderboard is ranked by total Good Points. If person A has 2,643 points and person B has 2,642 points, Person A will be ranked above Person B.

Group leaderboards (Teams, Regions, etc) are ranked by Total Good Points / Active-Participant-Days of activity. Intuitively, you can think of this as "average Good Points per person", except teams are not penalized for person-days with no data.

Here is a screencast that explains how this works in greater detail.