Facebook, Twiter, Myspace, Etc

I wonder with as much information we put on our Facebooks, Twitter, Myspace, Etc if it's really that safe. I've seen a lot of crazy stuff that people tend to put on their pages and they wonder how people aside from their friends know so much about them. I think that Facebook in general is smart to have a privacy button on what you wnt to show when friends and family are searching for you. Also it's smart so that way people who don't know you can't see anything unless you add them as a friend. This will help keep people who you don't know or like from seeing everything on your Facebook, Twitter, Myspace, Ect which is really helpful in most cases.