Facebook is huge and growing every day. And a lot of people have concerns about privacy. Others don't think about privacy on such sites at all (which is a big problem).
Facebook can be used safely, but people should educate themselves about privacy matters. Here is a good article with some general guidelines on Facebook called 5 Easy Steps to Stay Safe (and Private!) on Facebook. The article shows you how to configure your privacy settings to keep your information private, and there are some common sense guidelines about watching what you put online in the first place.
In Facebook, there are lots of quizzes you take on politics, pop culture, etc. These quizzes can be loads of fun, or a complete waste of time. There are privacy concerns about these quizzes, so here's another article, calledWhat Facebook Quizzes Know About You
To round out this Facebook-focused post, here's a link to a prior blog post of mine about Facebook using your photos in random ads.
The library uses Facebook, so if you're already on, or if you choose to join, come to the library's page and become a fan!