Which social media platforms seem geared towards personal use and which ones seem to work better for business?

I have some background with a lot of different social media platforms.  I have an account with twitter, tumblr, pinterest, LinkedIn, Facebook, Good Reads, PulseIt....and those are just the ones I remember that I have.  Playing around on all these, I think they can all be used for personal and business depending on what business you are in.

For example, I know many authors who are independent authors.  These people rely on social media to get word out about their book.  My first instinct is to say something like Good Reads or PulseIt are purely personal.  That's not true when you're an author.  Those reviews, people adding books their shelves, this is the bread and butter for an author.  If you're doing something like working in waste disposal then these platforms don't do you much good.

LinkedIn should be strictly business.  I've noticed that it seems to be a popularity contest, too.  I have been contacted by people I do not know who do not have a connection to me wanting to add me to their contacts.  Why?  I don't know them and they don't know me but here we are.

Twitter started out being personal.  Here again, I know a lot of authors and publicists who launch massive tweet campaigns to get the word out about a new novel or new product.

While I believe that all of these platforms started out for personal use, I believe that they are all being used for business now.  Facebook is the biggest of them and it's my opinion that many of these platforms are simply following Facebook's lead.