Hi. I'm on FB and it's a really good site for keeping in 'real time' touch with people. It started as a college site in US for people to keep in touch and network and then extended to WWW.
you can add whatever you like but it is not public unless you set it up that way. i have loads of pics and details of things we're doing and arrange things with friends and family on there BUT ONLY MY FRIENDS CAN SEE IT. you can set every aspect of who sees what via profile and privacy settings.
It's being compared to MySpace in the media but they're quite different.
I have to be honest - I love it!! It's like MN with more functionality and not targeted to any particular type.
have a look - you may be pleasantly surprised Facebook
And etiquette and good manners would usually mean that your photo and anything about you is not posted without your OK so, YES, i would definitely let the person know that you're not comfortable with your photo being up there.
Hope this explains a bit what it's all about