There is a lot of crap on Facebook, no doubt about it. I just visit it once a day for a quick browse. I don't do any of the games or surveys or countless other applications. There are usually funny photos that get posted or silly things people I know like to 'share'. Like: Do we really need a Lysol product scented like Lavender? Wouldn't the scent put you to sleep before you finish the kitchen floor? (silly stuff like that) Also my Facebook friends often share interesting news articles. (I think it's dangerous to complain about work, however...and I am always amazed that some people don't see the danger in THAT. Like the nitwits you mentioned...IT'S PUBLIC INFORMATION!)
What purpose it serves is in how you use it, same as the internet in general.
I use Facebook as a tool to get my art/music out and build up my fan base, as well as using some other sites. I keep up with fellow musicians, artists, cannabis activists, scientists, atheists and more. Having performed on cruise ships for 20 years, it is the easiest way for me to keep in contact with some of the many thousands of people I've met from around the world. As well as family and friends from school and elswhere.
I've never played a game like Farmville, Mafia Wars or any of those time wasters. I actually block each game request as I get them- so get less and less requests.
I use it to read and post links to things I find important- be it atheism/religion, failed cannabis/drug war policy, politics, music, art or whatever. I don't get many religious posts on my FB (and I have over 2,500 "friends"-80% I actually know), and those are not directed at me.
If someone doesn't like something I say or post and if I lose a "friend" on FB from it- I wouldn't even know who "unfriended" me unless they told me. The number of friends moves a few up or down every day - loose one- gain two- but it doesn't show who is no longer a "friend".
If you're bored of it, OK, don't use it, or check it infrequently, or inactivate your account- but getting pictures and all the rest of your stuff off of FB is harder than just inactivating your account.
See my illusion-filled sm'ART on Facebook or at http://www.kelinsmart.com