I've been living without FB for a few years now. I'm so much happier and more productive without it-- I was wasting a lot of time mindlessly scrolling through the feed several times a day.
One thing I notice is the chronic Facebookers who post every detail about their lives just assume I know what's going on when we meet up in real life. One friend was telling me about her injuries from a car accident and I had no idea she was ever in an accident. She was so surprised I didn't know, and we figured out it's because I'm not on Facebook. I also miss out on invitations, most of which are MLM parties or the like, so I'm not missing a whole lot.
As for what others miss-- I get a lot of flack for not having FB and posting pictures of my kid for my family and friends to "like," but I want to respect his privacy as much as I respect my own. It's hard for people to understand that, considering he's so young. As if being a child doesn't entitle someone to their own personal privacy.
That being said, nothing would ever make me log on again.