Facebook is notorious for collecting data on its users. They earn money from your data. They won't steal your credit card number, but they haven't always respected the privacy concerns of the users (or their friends, or their friends' friends).
Some scams (like they did a whole Temple Run Facebook thing which was just a massive scam) and if you look at Richard Stallman's blog, I don't like Stallman but he has many, many points about privacy issues with Facebook. I don't really care but that is why privacy on Facebook gets a '40' from me. They have sorted out many things but they still have 'problems' occasionally and have had MANY in the past.
ich mag facebook gar nicht, die werbungen nerven, die anfragen nerven, die bugs nerven.
google+ ist da viel weiter, leider nicht bekannt genug bei denen, die sich nicht so viel mit dem internet beschäftigen
Existem alguns aplicativos com vírus,não clique em links desconhecidos,principalmente os que oferencem algum programa,etc..
Fora isso gosto do facebook por causa de umas páginas interessantes e úteis para aumentar o conhecimento.