Blog Assessment

Hmmm...how to assess this?  I'm still trying to figure out exactly what the difference is between a blog, a social networking site, or a members only review posting site.  They all seem to have alot in common, in fact isn't the same basis used for each?  Okay, a blog is a site where you give out information and then people who are "following" you are allowed to comment.  Still sounds like facebook to me.  I like networking sites, there just seems to be so many of them.  How do you find the one that best suits you?  Keeping up with all of them seems impossible.  So...to answer this question I am going online to do alittle research and find out what the difference is.  More posting to follow :-)