It totally depends on the format of Groups there, and again the seriousness of people on being active there. When people join Fora, say 15-25% of people intend to participate there & be "Active". Whereas that doesnt happen in Groups on Social networking sites. On Orkut, we had around 3 lakh members in the Community, and about 50-60 of us were regularly active. Thats even when Orkut had not started in die out.