The weekly leaderboard, accessible by the "Leaders" icon at in the Flash application header bar, is an ongoing ranking of user activity, as determined by weekly point accumulation.  Points are gained by social activities such as chatting, visiting scenes, giving gifts to friends.  These points count towards your lifetime point total, and all points accumulated between Wednesday 12:00AM of one week to Tuesday 11:59PM PST of the following week go towards your weekly leaderboard ranking.

On the "Friends" tab of the weekly leaderboard pop-up, you can view your ranking in relationship to your top 9 ranked friends.  Clicking on the "Everyone" tab will show your ranking with respect to the week's top 10 point-earning users.