I use Facebook with privacy settings for friends and family only. It's great to connect with overseas families and friends. I don't have zillions of "friends" like the young ones, and those that I do have are all personally known to me. It's great to keep up with each other's news, and certainly saves a lot of emails as well.
I also belong to the Quebec Family History closed group on Facebook. A volunteer on there took photos of several of my family graves in the Mount Royal Cemetery for a small donation. I had originally had a Findagrave request in for about 3 years, had given them the detailed grave plot locations, but never had a result from there. Not only did this kind volunteer take photos of the graves, headstones etc, she also took extra photos of the surrounding areas, and also provided me with a transcription from a couple of the graves that were quite badly eroded.
It's a closed group, and one has to apply to join, but that wasn't an issue. But it's been very helpful to me. I believe there are more groups like that in different places in the World, but that's the only one I'm in.
I used to belong to one here in NZ called Old Friends, I think maybe it was an offshoot of Friends Reunited, with schools, works places, areas etc. That was free too, and contact was made with quite a good number of old friends and workmates. We had some great meet-ups too.
I think a lot of people were disappointed when that closed down, but Facebook has more appeal I think, especially for the youngsters, with being able to connect with more people around the world. But I do think they need to be a little more careful with some of the content they post!