As far as I can tell, the Social Networking feature shows up on the main forum which ones are online. It makes it easier to PM them or just to know when they are online. I haven't seen an official announcement of the feature, but that's as far as I can tell.
That's exactly why I made the annoucnement Kurt. I saw someone's Visitor Message and wondered if they knew the entire forum could see their message.
I'm assuming that it would be a nice feature to have to say something like "Your tanks look fantastic!" or maybe "Excellent seller!" Kind of a public feedback for the person. Again, just a guess though.