facebook.comは安全ですか？

Terribly intrusive. They will readily share your information EVERYWHERE, WITH EVERYONE, and WITHOUT TELLING YOU. Be extremely careful here, they'll disseminate your GPS coordinates around the world by default, and you'll never know because they're not going to tell you. Your physical safety is severely jeopardized if you're a facebook regular and anyone with tech savvy knows your name. Not to mention that most of the functions you have no control over, and all of them default towards spreading your information everywhere without telling you.

Facebook's owner, Mark Zuckerberg, has publicly stated his belief that users do not care about privacy, and Facebook behaves accordingly. I do not trust Facebook with personal information beyond what they absolutely require to create an account. Facebook has a long record of playing fast and loose with users' data, and they have only improved privacy issues when forced to by market pressure, or legal means.