When you sign up it asks you if you want to invite your friends (from your email contacts list i.e. hotmail, gmail) If you say yes, it will send an invitation to all you email contacts. It will also tell you who from your email contacts is already a member

I think Facebook is generally a good thing. Its connected me with people I thought I would never have contact with again. The privacy settings are pretty good if your not interested in people seeing particular things about you. Plus people cant view your profile if you havent accepted them as a friend (i think). You can also stop it being 'Google searchable'.