My main beef with FB and G+ are that conversations don't seem to last long. I like that with a message board a conversation can go for months or years and people can drop in and out with their comments, and you occasionally get fresh blood with something constructive or fun to say.
Facebook conversations drop away too quickly.
Most modern social media is all about fitting the context of a smart phone, which means small words, small sentences and more timely discussion. That means no lengthy posts, no continuance of old threads, and definitely no back-and-forth conversation. It's all about PUSH content rather than PULL.