I'm picking up your cynicism and I've got plenty of complaints about Facebook myself (mostly related to how it's a closed-off system that requires you to use their service to communicate with people, unlike email where you can choose your provider/host and still communicate with people who prefer others).
That said, the idea that you automatically use such services for shallow, mass communication with large numbers of fleeting friends is sort of disingenuous. I keep an account there because like many people, it's a fairly effective way to coordinate with friends and family without creating long email chains or massive group texts.
Not everyone is trying to be a social butterfly, resigning themselves to quantity over quality or neglecting sleep and hobbies. Plenty of us have people we'd like to keep in touch with and a place to announce events (cookouts or parties we're holding, concerts or camping trips we're attending, etc) so our other friends and acquaintances can find out about them and join us in person.
I've currently got a closed group on there where 4 or 5 of us have been sharing our progress on some neat electronic art projects we're working on. It's not something we use at the expense of hobbies and interests but rather a common tool for us to casually collaborate and share the things we're interested in and working on.
So yeah, I'd love if I could use Google+ or some other service where I like the interface and features better and I'd love if that didn't require everyone to "jump ship" at the same time. A common protocol between social forums (again, like email) would go a long way toward addressing the complaints I have with them.
But since that's not likely to happen, I'll take occasionally checking my Facebook accounts for things people have shared with me over missing out on those conversations due to distance or personal time constraints. I don't live on Facebook but I stop by a few times a week when I feel like looking at Facebook. Haven't lost any sleep over it yet and I've developed quite a few hobbies around the communication that FB and other services foster.