- family & close friends
- acquaintances & loose friends
- school alum
- social groups / clubs
- those who you might work with/for
- linked in, you failed this audience
- interests beyond clubs, outside acquantances
No social network does a good job at allowing a person to share with those groups as desired. What I share on twitter is far more techie than what my friends/family on FB care about (mental note, disconnect twitter from fb). What I follow on twitter doesn't line up with what I post (I also see way to much to actually track twitter or fb, I pop in every few days, and only see the top of the feed). most of the people on FB are more acquaintances or past friends from social groups, and some family.The reality is that what will probably "win" will be a few discrete social networks... one for your career (probably not linkedin), a new one for your family and close friends, facebook for your loose friends and acquantences... and something closer to bulletin boards and/or webchat for social interest groups (probably not meetup).
I don't think the one site to rule them all will survive in the long run. And those groups trying to do so with facebook, twitter and pinterest are failing... those trying to build business models that aren't bought are failing.