I see that many people have left forums and moved to social network (SN).? I see that many prefer to chat so much stuff in facebook, LN, Twitter compared to so less in forums. Years ago before social networks, there was a huge activity in all the forums such as DP, warrior etc.
I think some people have migrated from forums to Social Media like Facebook, Twitter, etc. Forums are still a wonderful wealth of information and some forums like this one still have an active community.
I think SN's target and segment a different type or market or person. For individuals who frequented forums solely for entertainment or socializing purposes might of left but for individuals who are serious marketers or niche for that matter stayed.