Facebook Issues

Ok, new gripe.
I was thinking today about what to write for my second blog when it occurred to me that I still don't understand Facebook.
I originally got sent an invitation to an exhibition that my friend was part of. To reply to it, I had to sign up to Facebook. That was all fine until I was sent another email requesting that I update my profile so that others could find me if they were searching. I was a little worried as to why any one would be searching for me, it's not like I'm famous or anything.
Ever since then I have had constant emails about updates of friends pages, people who would like to become my friends (people I have never met in my life) and just random requests from people who decided I might like to play a game they have played or a quiz that they did.
Please guys, I just don't care!
So someone, if you care enough about Facebook and wish to defend it, then please explain what the attraction is.

Blogging

Can someone explain to me the point of a blog?
Many times I have wondered and still no one can answer me?
How many people actually spend their time on the internet, writing about themselves, just so that the whole world can know who they are and why they think they are important?
Please explain.