My kids use the site too. I have talked to them since the day we got our first computer about not giving out too much information and all I can do is hope that it sunk in.
In defense of my space, my children have found long lost friends that have moved away, and since we moved away also it helps them to stay in touch with their old friends and school mates. I hate that it is being abused by the pervs. But then, what isn't?