Facebook - what do you use it for?

I spend a lot of time on Facebook lately, running it in the background as I work on other things, and I have noticed that the people that use it tend to use it for a wide range of things.

It seems to be able to be broke down into a broad range of uses:

• Keeping up with what friends and/or family are up to
• Spreading a political message
• Spreading a religious message
• Spreading a non-political / non-religious message
• Playing games
• Keeping up with what celebraties are doing
• Advertising product / service / website / etc
• Sharing gossip with anyone that will listen
• An open diary of everything the poster has done during the day
• Brag about something that happened to try to impress others

And there are a few more trends that I have noticed. Those are the basic broad baseline for things that I have noticed people  use Facebook for. I use it to keep up with what friends and extended family are up to, and to play games. FarmVille and Bejeweled Deluxe are my most common addictions.

So, my question, do you use Facebook? Is so, what do you use it for? If not, why haven't you joined the site yet? (I had left it for a while as consuming too much time.)