I am with Skinny on this one. I have a friends all over the country and it is simply just easier to stay in touch with everyone. I use the IM feature a lot on FB. It is really nice to be able to have a short conversation with someone just to see how they are doing.
Linkedin is great for business contacts and stay up with were people are in there careers. I would say that my FB accounts and linkedin accounts differ greatly with who I am connected with on each site.
But the social marketing thing IMO is crap. I have never cared about any of it. I don’t even care all that much about the company I work for post. They asked me to join for social media marking purposes that was fine there pretty much the only company I follow. But I don’t think it gets them very much. They get really concerned with how many people they have following them. I don’t think it matters if you have a million people following you or hundred thousand it makes little difference.