Great idea to increase active member participation in social networks

Add a "recommended groups" feature, something like "people who join this group also join these other groups". Or a different flavor, such as "your connections have joined the following groups" (just list the top 3 or top 5 groups).

It's very easy to implement: for each member, create a list of candidate groups, score / rank these groups according to some criterion (e.g. proportion of your friends belonging to a specific group, or metric measuring similarity between 2 groups), and suggest the top 3 groups. So far I've not seen this powerful feature implemented yet on LinkedIn or Facebook.

It is also possible to suggest potential groups to members having 0 friend and belonging to 0 group, as long as their profiles are keyword-rich.