Is Facebook a good thing or merely a timewaster?

Having had a Faeebook account for a few years now (off and on), I sometimes wonder if it is a good thing to have. Yes, I have developed some real-life friends via Facebook, people whom I actually know in real life, but I also spend too much time on it, when I could probably be doing something more constructive.
I tend to use my FB account as a type of diary, and maybe this is giving too much away. On the other hand, I enjoy the social interaction of it, and sometimes,online chatting. FB can be a place of bullying, but it doesn't have to be. If any of my FB friends, people I know in real life or not, make rude or abusive comments, they are normally let go. But I've only had to do this a few times in four years, which is not bad. If I keep FB in perspective and use it only sparingly, this feels about right. It's also a good way of sharing events, reviewing films, books, concerts,  etc, which is neat. And of course, you can limit your time on FB, self-regulate or just stay away altogether!