Hover over the Groups tab and there is a link for active groups. The active groups are divided into 5 lists, groups with a lot of hits (most popular), groups with a lot of activity (most conversations), group with a large percentage of friends (most friendships), groups up and coming (rising stars) and CM owned groups.
If you are looking for active groups then most conversations and rising stars is a great place to look for private groups. The CM groups are all public. They are active and tend to have a bit more drama. If you are looking to make friends then the friendships groups are great. Most are small and active but they can also be exclusive. The Most popular groups will tell you which groups are getting buzz. as they are generating the most views. This could be because they are really active have really good games and contests or because they have great promotion.
at 7:39 PM on Aug. 1, 2010