Popular Quests

It seems as though the list of popular quests is determined by the number of users subscribed to the quest. First I would think the more items would make it more active, but most all there needs to be a "fade" mechanism to take popular quests that noone has contributed to or visited in a long time and reduce their popularity. Perhaps a method of points... 10 points for every user on the quest, 15 points for every item on the quest times minus 5% for every day noone is active on it?

Just a though... those quests have been there FOREVER.