It looks to me like the biggest problem is that people seem to have very boring or annoying or pointless Facebook 'friends'. Perhaps thinking about who you think of as a friend and why would be more useful than complaining about how you communicate with those friends. I fell into the trap of just adding people a few years back, but then
I went through my 'friends' and decided who it was who I actually wanted to hear from and really liked or valued, and got rid of all the rest. I now have a steady 200 or so* FB friends, a mix of local connections, a few family, and old friends from around the world, and I'm quite happy with that (*coincidentally or not, this is not far off Dunbar's numbers, which should please
@GaryA...).
Twitter is a whole different story. I basically use Twitter for interesting notifications in my field of work. It means journalists and other academics get in touch with me and vice-versa and it's very useful.
I don't use professional networks like LinkedIn, which IMHO are the worst and most pointless of all social networks. But then I'm not looking for a job...