I joined LJ just as it was cresting in popularity. A lot of people added me, and I them, but many of those who are still officially on my friends list no longer post anything. Probably most have switched to Facebook and/or Twitter. I do an RSS feed of my public LJ posts to my FB page, but otherwise do almost no original FB posts. My only reason for being on FB is to connect with people who do FB instead of LJ and who want to stay in touch.
Me, I prefer LJ. It's easier to work with, has a more pleasing visual presentation, and -- the biggie -- it allows one to post and comment at greater length than FB or Twitter. Most of my posts aren't that long, but some are. And I like the fact that people can comment on original posts and also reply to each other's comments. It is both more literary and more conversational than the other sites. But then, that's the difference between blogging and social networking, I guess.
Anyway, Happy Birthday to The Daily Mustard! Long live my blog!